Targeted pyrrolobenzodiazapine conjugates

ABSTRACT

Provided are Conjugate comprising PBDs conjugated to a targeting agent and methods of using such PBDs.

The present invention relates to targeted pyrrolobenzodiazepine (PBD) conjugates, in particular pyrrolobenzodiazepine dimers that are conjugated to a targeting agent via the C2 position of one of the monomers.

BACKGROUND TO THE INVENTION

Some pyrrolobenzodiazepines (PBDs) have the ability to recognise and bond to specific sequences of DNA; the preferred sequence is PuGPu. The first PBD antitumour antibiotic anthramycin, was discovered in 1965 (Leimgruber, et al., J. Am. Chem. Soc., 87, 5793-5795 (1965); Leimgruber, et al., J. Am. Chem. Soc., 87, 5791-5793 (1965)). Since then, a number of naturally occurring PBDs have been reported, and over 10 synthetic routes have been developed to a variety of analogues (Thurston, et al., Chem. Rev. 1994, 433-465 (1994)). Family members include abbeymycin (Hochlowski, et al., J. Antibiotics, 40, 145-148 (1987)), chicamycin (Konishi, et al., J. Antibiotics, 37, 200-206 (1984)), DC-81 (Japanese Patent 58-180 487; Thurston, et al., Chem. Brit., 26, 767-772 (1990); Bose, et al., Tetrahedron, 48, 751-758 (1992)), mazethramycin (Kuminoto, et al., J. Antibiotics, 33, 665-667 (1980)), neothramycins A and B (Takeuchi, et al., J. Antibiotics, 29, 93-96 (1976)), porothramycin (Tsunakawa, et al., J. Antibiotics, 41, 1366-1373 (1988)), prothracarcin (Shimizu, et al, J. Antibiotics, 29, 2492-2503 (1982); Langley and Thurston, J. Org. Chem., 52, 91-97 (1987)), sibanomicin (DC-102) (Hara, et al., J. Antibiotics, 41, 702-704 (1988); Itoh, et al., J. Antibiotics, 41, 1281-1284 (1988)), sibiromycin (Leber, et al., J. Am. Chem. Soc., 110, 2992-2993 (1988)) and tomamycin (Arima, et al., J. Antibiotics, 25, 437-444 (1972)). PBDs are of the general structure:

They differ in the number, type and position of substituents, in both their aromatic A rings and pyrrolo C rings, and in the degree of saturation of the C ring. In the B-ring there is either an imine (N═C), a carbinolamine(NH—CH(OH)), or a carbinolamine methyl ether (NH—CH(OMe)) at the N10-C11 position, which is the electrophilic centre responsible for alkylating DNA. All of the known natural products have an (S)-configuration at the chiral C11a position which provides them with a right-handed twist when viewed from the C ring towards the A ring. This gives them the appropriate three-dimensional shape for isohelicity with the minor groove of B-form DNA, leading to a snug fit at the binding site (Kohn, In Antibiotics Ill. Springer-Verlag, New York, pp. 3-11 (1975); Hurley and Needham-VanDevanter, Acc. Chem. Res., 19, 230-237 (1986)). The ability of PBDs to form an adduct in the minor groove enables them to interfere with DNA processing, hence their use as antitumour agents.

The biological activity of these molecules can be potentiated by joining two PBD units together through their C8/C′-hydroxyl functionalities via a flexible alkylene linker (Bose, D. S., et al., J. Am. Chem. Soc., 114, 4939-4941 (1992); Thurston, D. E., et al., J. Org. Chem., 61, 8141-8147 (1996)). The PBD dimers are thought to form sequence-selective DNA lesions such as the palindromic 5′-Pu-GATC-Py-3′ interstrand cross-link (Smellie, M., et al., Biochemistry, 42, 8232-8239 (2003); Martin, C., et al., Biochemistry, 44, 4135-4147) which is thought to be mainly responsible for their biological activity. One example of a PBD dimer is SG2000 (SJG-136):

(Gregson, S., et al., J. Med. Chem., 44, 737-748 (2001); Alley, M. C., et al., Cancer Research, 64, 6700-6706 (2004); Hartley, J. A., et al., Cancer Research, 64, 6693-6699 (2004)).

Due to the manner in which these highly potent compounds act in cross-linking DNA, PBD dimers have been made symmetrically, i.e., both monomers of the dimer are the same. This synthetic route provides for straightforward synthesis, either by constructing the PBD dimer moiety simultaneously having already formed the dimer linkage, or by reacting already constructed PBD monomer moieties with the dimer linking group. These synthetic approaches have limited the options for preparation of targeted conjugates containing PBDs. Due to the observed potency of PBD dimers, however, there exists a need for PBD dimers that are conjugatable to targeting agents for use in targeted therapy.

DISCLOSURE OF THE INVENTION

The present invention relates to Conjugates comprising dimers of PBDs linked to a targeting agent, wherein a PBD monomer has a substituent in the C2 position that provides an anchor for linking the compound to the targeting agent. The present invention also relates to Conjugates comprising dimers of PBDs conjugated to a targeting agent, wherein the PBD monomers of the dimer are different. One of PBD monomers has a substituent in the C2 position that provides an anchor for linking the compound to the targeting agent. The Conjugates described herein have potent cytotoxic and/or cytostatic activity against cells expressing a target molecule, such as cancer cells or immune cells. These conjugates exhibit good potency with reduced toxicity, as compared with the corresponding PBD dimer free drug compounds.

In some embodiments, the Conjugates have the following formula I:

L-(LU-D)p   (I)

wherein L is a Ligand unit (i.e., a targeting agent), LU is a Linker unit and D is a Drug unit comprising a PBD dimer. The subscript p is an integer of from 1 to 20. Accordingly, the Conjugates comprise a Ligand unit covalently linked to at least one Drug unit by a Linker unit. The Ligand unit, described more fully below, is a targeting agent that binds to a target moiety. The Ligand unit can, for example, specifically bind to a cell component (a Cell Binding Agent) or to other target molecules of interest. Accordingly, the present invention also provides methods for the treatment of, for example, various cancers and autoimmune disease. These methods encompass the use of the Conjugates wherein the Ligand unit is a targeting agent that specifically binds to a target molecule. The Ligand unit can be, for example, a protein, polypeptide or peptide, such as an antibody, an antigen-binding fragment of an antibody, or other binding agent, such as an Fc fusion protein.

In a first aspect, the Conjugates comprise a Conjugate of formula I (supra), wherein the Drug unit comprises a PBD dimer of the following formula II:

wherein:

R² is of formula III:

where A is a C₅₋₇ aryl group, X is an activatable group for conjugation to the Linker unit, wherein X is selected from the group comprising: —O—, —S—, —C(O)O—, —C(O)—, —NHC(O)—, and —N(R^(N))—, wherein R^(N) is selected from the group comprising H, C₁₋₄ alkyl and (C₂H₄O)_(m)CH₃, where m is 1 to 3, and either:

-   -   (i) Q¹ is a single bond, and Q² is selected from a single bond         and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S         and NH and n is from 1 to 3; or     -   (ii) Q¹ is —CH═CH—, and Q² is a single bond;

R¹² is a C₅₋₁₀ aryl group, optionally substituted by one or more substituents selected from the group comprising: halo, nitro, cyano, ether, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene;

R⁶ and R⁹ are independently selected from H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo;

where R and R′ are independently selected from optionally substituted C₁₋₁₂ alkyl, optionally substituted C₃₋₂₀ heterocyclyl and optionally substituted C₅₋₂₀ aryl groups;

R⁷ is selected from H, R, OH, OR, SH, SR, NH₂, NHR, NHRR′, nitro, Me₃Sn and halo; either:

-   -   (a) R¹⁰ is H, and R¹¹ is OH or OR^(A), where R^(A) is C₁₋₄         alkyl;     -   (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the         nitrogen and carbon atoms to which they are bound; or     -   (c) R¹⁰ is H and R¹¹ is SO_(z)M, where z is 2 or 3 and M is a         monovalent pharmaceutically acceptable cation;

R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more heteroatoms, e.g. O, S, NR^(N2) (where R^(N2) is H or C₁₋₄ alkyl), and/or aromatic rings, e.g. benzene or pyridine;

Y and Y′ are selected from O, S, or NH;

R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R¹⁰ and

R^(11′) are the same as R¹⁰ and R¹¹, wherein if R¹¹ and R^(11′) are SO_(z)M, M may represent a divalent pharmaceutically acceptable cation.

In a second aspect, the use of the Conjugate of formula I is provided for the manufacture of a medicament for treating a proliferative disease or autoimmune disease. In a related third aspect, the use of the Conjugate of formula I is provided for the treatment of a proliferative disease or an autoimmune disease.

In another aspect there is provided the use of a Conjugate of formula I to provide a PBD dimer, or a salt or solvate thereof, at a target location.

One of ordinary skill in the art is readily able to determine whether or not a candidate conjugate treats a proliferative condition for any particular cell type. For example, assays which may conveniently be used to assess the activity offered by a particular compound are described in the examples below.

The term “proliferative disease” pertains to an unwanted or uncontrolled cellular proliferation of excessive or abnormal cells which is undesired, such as, neoplastic or hyperplastic growth, whether in vitro or in vivo.

Examples of proliferative conditions include, but are not limited to, benign, pre-malignant, and malignant cellular proliferation, including but not limited to, neoplasms and tumours (e.g., histocytoma, glioma, astrocyoma, osteoma), cancers (e.g. lung cancer, small cell lung cancer, gastrointestinal cancer, bowel cancer, colon cancer, breast carinoma, ovarian carcinoma, prostate cancer, testicular cancer, liver cancer, kidney cancer, bladder cancer, pancreatic cancer, brain cancer, sarcoma, osteosarcoma, Kaposi's sarcoma, melanoma), leukemias, psoriasis, bone diseases, fibroproliferative disorders (e.g. of connective tissues), and atherosclerosis. Other cancers of interest include, but are not limited to, haematological; malignancies such as leukemias and lymphomas, such as non-Hodgkin lymphoma, and subtypes such as DLBCL, marginal zone, mantle zone, and follicular, Hodgkin lymphoma, AML, and other cancers of B or T cell origin.

Examples of autoimmune disease include the following: rheumatoid arthritis, autoimmune demyelinative diseases (e.g., multiple sclerosis, allergic encephalomyelitis), psoriatic arthritis, endocrine ophthalmopathy, uveoretinitis, systemic lupus erythematosus, myasthenia gravis, Graves' disease, glomerulonephritis, autoimmune hepatological disorder, inflammatory bowel disease (e.g., Crohn's disease), anaphylaxis, allergic reaction, Sjögren's syndrome, type I diabetes mellitus, primary biliary cirrhosis, Wegener's granulomatosis, fibromyalgia, polymyositis, dermatomyositis, multiple endocrine failure, Schmidt's syndrome, autoimmune uveitis, Addison's disease, adrenalitis, thyroiditis, Hashimoto's thyroiditis, autoimmune thyroid disease, pernicious anemia, gastric atrophy, chronic hepatitis, lupoid hepatitis, atherosclerosis, subacute cutaneous lupus erythematosus, hypoparathyroidism, Dressler's syndrome, autoimmune thrombocytopenia, idiopathic thrombocytopenic purpura, hemolytic anemia, pemphigus vulgaris, pemphigus, dermatitis herpetiformis, alopecia areata, pemphigoid, scleroderma, progressive systemic sclerosis, CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia), male and female autoimmune infertility, ankylosing spondolytis, ulcerative colitis, mixed connective tissue disease, polyarteritis nedosa, systemic necrotizing vasculitis, atopic dermatitis, atopic rhinitis, Goodpasture's syndrome, Chagas' disease, sarcoidosis, rheumatic fever, asthma, recurrent abortion, anti-phospholipid syndrome, farmer's lung, erythema multiforme, post cardiotomy syndrome, Cushing's syndrome, autoimmune chronic active hepatitis, bird-fancier's lung, toxic epidermal necrolysis, Alport's syndrome, alveolitis, allergic alveolitis, fibrosing alveolitis, interstitial lung disease, erythema nodosum, pyoderma gangrenosum, transfusion reaction, Takayasu's arteritis, polymyalgia rheumatica, temporal arteritis, schistosomiasis, giant cell arteritis, ascariasis, aspergillosis, Sampter's syndrome, eczema, lymphomatoid granulomatosis, Behcet's disease, Caplan's syndrome, Kawasaki's disease, dengue, encephalomyelitis, endocarditis, endomyocardial fibrosis, endophthalmitis, erythema elevatum et diutinum, psoriasis, erythroblastosis fetalis, eosinophilic faciitis, Shulman's syndrome, Felty's syndrome, filariasis, cyclitis, chronic cyclitis, heterochronic cyclitis, Fuch's cyclitis, IgA nephropathy, Henoch-Schonlein purpura, graft versus host disease, transplantation rejection, cardiomyopathy, Eaton-Lambert syndrome, relapsing polychondritis, cryoglobulinemia, Waldenstrom's macroglobulemia, Evan's syndrome, and autoimmune gonadal failure.

In some embodiments, the autoimmune disease is a disorder of B lymphocytes (e.g., systemic lupus erythematosus, Goodpasture's syndrome, rheumatoid arthritis, and type I diabetes), TH1-lymphocytes (e.g., rheumatoid arthritis, multiple sclerosis, psoriasis, Sjögren's syndrome, Hashimoto's thyroiditis, Graves' disease, primary biliary cirrhosis, Wegener's granulomatosis, tuberculosis, or graft versus host disease), or Th2-lymphocytes (e.g., atopic dermatitis, systemic lupus erythematosus, atopic asthma, rhinoconjunctivitis, allergic rhinitis, Omenn's syndrome, systemic sclerosis, or chronic graft versus host disease). Generally, disorders involving dendritic cells involve disorders of Th1-lymphocytes or Th2-lymphocytes. In some embodiments, the autoimmune disorder is a T cell-mediated immunological disorder.

In a fourth aspect of the present invention comprises a method of making the Conjugates formula I.

The dimeric PBD compounds for use in the present invention are made by different strategies to those previously employed in making symmetrical dimeric PBD compounds. In particular, the present inventors have developed a method which involves adding each C2 aryl substituent to a symmetrical PBD dimer core in separate method steps, Accordingly, a sixth aspect of the present invention provides a method of making a Conjugate of formula I, comprising at least one of the method steps described herein.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 to 6 show the effect of conjugates of the present invention in tumours.

DEFINITIONS

When a trade name is used herein, reference to the trade name also refers to the product formulation, the generic drug, and the active pharmaceutical ingredient(s) of the trade name product, unless otherwise indicated by context.

Binding Agent and Targeting Agent

The terms “binding agent” and “targeting agent as used herein refer to a molecule, e.g., protein, polypeptide or peptide, that specifically binds to a target molecule. Examples can include a full length antibody, an antigen binding fragment of a full length antibody, other agent (protein, polypeptide or peptide) that includes an antibody heavy and/or light chain variable region that specifically bind to the target molecule, or an Fc fusion protein comprising an extracellular domain of a protein, peptide polypeptide that binds to the target molecule and that is joined to an Fc region, domain or portion thereof, of an antibody.

Specifically Binds

The terms “specifically binds” and “specific binding” refer to the binding of an antibody or other protein, polypeptide or peptide to a predetermined molecule (e.g., an antigen). Typically, the antibody or other molecule binds with an affinity of at least about 1×10⁷ M⁻¹, and binds to the predetermined molecule with an affinity that is at least two-fold greater than its affinity for binding to a non-specific molecule (e.g., BSA, casein) other than the predetermined molecule or a closely-related molecule.

Pharmaceutically Acceptable Cations

Examples of pharmaceutically acceptable monovalent and divalent cations are discussed in Berge, et al., J. Pharm. Sci., 66, 1-19 (1977), which is incorporated herein by reference.

The pharmaceutically acceptable cation may be inorganic or organic.

Examples of pharmaceutically acceptable monovalent inorganic cations include, but are not limited to, alkali metal ions such as Na⁺ and K⁺. Examples of pharmaceutically acceptable divalent inorganic cations include, but are not limited to, alkaline earth cations such as Ca ²⁺ and Mg²⁺. Examples of pharmaceutically acceptable organic cations include, but are not limited to, ammonium ion (i.e. NH₄ ⁺) and substituted ammonium ions (e.g. NH₃R⁺, NH₂R₂ ⁺, NHR₃ ⁺, NR₄ ⁺). Examples of some suitable substituted ammonium ions are those derived from: ethylamine, diethylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CH₃)₄ ⁺.

Substituents

The phrase “optionally substituted” as used herein, pertains to a parent group which may be unsubstituted or which may be substituted.

Unless otherwise specified, the term “substituted” as used herein, pertains to a parent group which bears one or more substituents. The term “substituent” is used herein in the conventional sense and refers to a chemical moiety which is covalently attached to, or if appropriate, fused to, a parent group. A wide variety of substituents are well known, and methods for their formation and introduction into a variety of parent groups are also well known.

Examples of substituents are described in more detail below.

C₁₋₁₂ alkyl: The term C₁₋₁₂ alkyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of a hydrocarbon compound having from 1 to 12 carbon atoms, which may be aliphatic or alicyclic, and which may be saturated or unsaturated (e.g. partially unsaturated, fully unsaturated). Thus, the term “alkyl” includes the sub-classes alkenyl, alkynyl, cycloalkyl, etc., discussed below.

Examples of saturated alkyl groups include, but are not limited to, methyl (C₁), ethyl (C₂), propyl (C₃), butyl (C₄), pentyl (C₅), hexyl (C₆) and heptyl (C₇).

Examples of saturated linear alkyl groups include, but are not limited to, methyl (C₁), ethyl (C₂), n-propyl (C₃), n-butyl (C₄), n-pentyl (amyl) (C₅), n-hexyl (C₆) and n-heptyl (C₇).

Examples of saturated branched alkyl groups include iso-propyl (C₃), iso-butyl (C₄), sec-butyl (C₄), tert-butyl (C₄), iso-pentyl (C₅), and neo-pentyl (C₅).

C₂₋₁₂ Alkenyl: The term “C₂₋₁₂ alkenyl” as used herein, pertains to an alkyl group having one or more carbon-carbon double bonds.

Examples of unsaturated alkenyl groups include, but are not limited to, ethenyl (vinyl, —CH═CH₂), 1-propenyl (—CH═CH—CH₃), 2-propenyl (allyl, —CH—CH═CH₂), isopropenyl (1-methylvinyl, —C(CH₃)═CH₇), butenyl (C₄), pentenyl (C₅), and hexenyl (C₆).

C₂₋₁₂ alkynyl: The term “C₂₋₁₂ alkynyl” as used herein, pertains to an alkyl group having one or more carbon-carbon triple bonds.

Examples of unsaturated alkynyl groups include, but are not limited to, ethynyl (—C≡CH) and 2-propynyl (propargyl, —CH₂—C≡CH).

C₃₋₁₂ cycloalkyl: The term “C₃₋₁₂ cycloalkyl” as used herein, pertains to an alkyl group which is also a cyclyl group; that is, a monovalent moiety obtained by removing a hydrogen atom from an alicyclic ring atom of a cyclic hydrocarbon (carbocyclic) compound, which moiety has from 3 to 7 carbon atoms, including from 3 to 7 ring atoms.

Examples of cycloalkyl groups include, but are not limited to, those derived from:

-   -   saturated monocyclic hydrocarbon compounds:

cyclopropane (C₃), cyclobutane (C₄), cyclopentane (C₅), cyclohexane (C₆), cycloheptane (C₇), methylcyclopropane (C₄), dimethylcyclopropane (C₅), methylcyclobutane (C₅), dimethylcyclobutane (C₆), methylcyclopentane (C₆), dimethylcyclopentane (C₇) and methylcyclohexane (C₇);

-   -   unsaturated monocyclic hydrocarbon compounds:

cyclopropene (C₃), cyclobutene (C₄), cyclopentene (C₅), cyclohexene (C₆), methylcyclopropene (C₄), dimethylcyclopropene (C₅), methylcyclobutene (C₅), dimethylcyclobutene (C₆), methylcyclopentene (C₆), dimethylcyclopentene (C₇) and methylcyclohexene (C₇); and

-   -   saturated polycyclic hydrocarbon compounds:

norcarane (C₇), norpinane (C₇), norbornane (C₇).

C₃₋₂₀ heterocyclyl: The term “C₃₋₂₀ heterocyclyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a ring atom of a heterocyclic compound, which moiety has from 3 to 20 ring atoms, of which from 1 to 10 are ring heteroatoms. Preferably, each ring has from 3 to 7 ring atoms, of which from 1 to 4 are ring heteroatoms.

In this context, the prefixes (e.g. C₃₋₂₀, C₃₋₇, C₅₋₆, etc.) denote the number of ring atoms, or range of number of ring atoms, whether carbon atoms or heteroatoms. For example, the term “C₅₋₆heterocyclyl”, as used herein, pertains to a heterocyclyl group having 5 or 6 ring atoms.

Examples of monocyclic heterocyclyl groups include, but are not limited to, those derived from:

N₁: aziridine (C₃), azetidine (C₄), pyrrolidine (tetrahydropyrrole) (C₅), pyrroline (e.g., 3-pyrroline, 2,5-dihydropyrrole) (C5), 2H-pyrrole or 3H-pyrrole (isopyrrole, isoazole) (C₅), piperidine (C₆), dihydropyridine (C₆), tetrahydropyridine (C₆), azepine (C₇);

O₁: oxirane (C₃), oxetane (C₄), oxolane (tetrahydrofuran) (C5), oxole (dihydrofuran) (C₅), oxane (tetrahydropyran) (C₆), dihydropyran (C₆), pyran (C₆), oxepin (C₇);

S₁: thiirane (C₃), thietane (C₄), thiolane (tetrahydrothiophene) (C₅), thiane (tetrahydrothiopyran) (C₆), thiepane (C₇);

O₂: dioxolane (C₅), dioxane (C₆), and dioxepane (C₇);

O₃: trioxane (C₆);

N₂: imidazolidine (C₅), pyrazolidine (diazolidine) (C₅), imidazoline (C₅), pyrazoline (dihydropyrazole) (C₅), piperazine (C₅);

N₁O₁: tetrahydrooxazole (C₅), dihydrooxazole (C₅), tetrahydroisoxazole (C₅), dihydroisoxazole (C₅), morpholine (C₆), tetrahydrooxazine (C₆), dihydrooxazine (C₆), oxazine (C₆);

N₁S₁: thiazoline (C₅), thiazolidine (C₅), thiomorpholine (C₆);

N₂O₁: oxadiazine (C₆);

O₁S₁: oxathiole (C₅) and oxathiane (thioxane) (C₆); and,

N₁O₁S₁: oxathiazine (C₆).

Examples of substituted monocyclic heterocyclyl groups include those derived from saccharides, in cyclic form, for example, furanoses (C₅), such as arabinafuranose, lyxofuranose, ribofuranose, and xylofuranse, and pyranoses (C₆), such as allopyranose, altropyranose, glucopyranose, mannopyranose, gulopyranose, idopyranose, galactopyranose, and talopyranose,

C₅₋₂₀ aryl: The term “C₅₋₂₀ aryl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from an aromatic ring atom of an aromatic compound, which moiety has from 3 to 20 ring atoms. Preferably, each ring has from 5 to 7 ring atoms.

In this context, the prefixes (e.g. C₃₋₂₀, C₅₋₇, C₅₋₆, etc.) denote the number of ring atoms, or range of number of ring atoms, whether carbon atoms or heteroatoms. For example, the term “C₅₋₆ aryl” as used herein, pertains to an aryl group having 5 or 6 ring atoms.

The ring atoms may be all carbon atoms, as in “carboaryl groups”,

Examples of carboaryl groups include, but are not limited to, those derived from benzene (i.e. phenyl) (C₆), naphthalene (C₁₀), azulene (C₁₀), anthracene (C₁₄), phenanthrene (C₁₄), naphthacene (C₁₈), and pyrene (C₁₆).

Examples of aryl groups which comprise fused rings, at least one of which is an aromatic ring, include, but are not limited to, groups derived from indene (e.g. 2,3-dihydro-1H-indene) (C₉), indene (C₉), isoindene (C₉), tetraline (1,2,3,4-tetrahydronaphthalene (C₁₀), acenaphthene (C₁₂), fluorene (C₁₃), phenalene (C₁₃), acephenanthrene (C₁₅), and aceanthrene (C₁₆).

Alternatively, the ring atoms may include one or more heteroatoms, as in “heteroaryl groups”. Examples of monocyclic heteroaryl groups include, but are not limited to, those derived from:

N₁: pyrrole (azole) (C₅), pyridine (azine) (C₆);

O₁: furan (oxole) (C₅);

S₁: thiophene (thiole) (C₅);

N₁O₁: oxazole (C₅), isoxazole (C₅), isoxazine (C₆);

N₂O₁: oxadiazole (furazan) (C₅);

N₃O₁: oxatriazole (C₅);

N₁S₁: thiazole (C₅), isothiazole (C₅);

N₂: imidazole (1,3-diazole) (C₅), pyrazole (1,2-diazole) (C₅), pyridazine (1,2-diazine) (C₆), pyrimidine (1,3-diazine) (C₆) (e.g., cytosine, thymine, uracil), pyrazine (1,4-diazine) (C₆);

N₃: triazole (C₅), triazine (C₆); and,

N₄: tetrazole (C₅).

Examples of heteroaryl which comprise fused rings, include, but are not limited to:

-   -   C₉ (with 2 fused rings) derived from benzofuran (C₁),         isobenzofuran (C₁), indole (N₁), isoindole (N₁), indolizine         (N₁), indoline (N₁), isoindoline (N₁), purine (N₄) (e.g.,         adenine, guanine), benzimidazole (N₂), indazole (N₂),         benzoxazole (N₁O₁), benzisoxazole (N₁O₁), benzodioxole (O₂),         benzofurazan (N₂O₁), benzotriazole (N₃), benzothiofuran (S₁),         benzothiazole (N₁S₁), benzothiadiazole (N₂S);     -   C₁₀ (with 2 fused rings) derived from chromene (C₁), isochromene         (C₁), chroman (O₁), isochroman (O₁), benzodioxan (O₂), quinoline         (N₁), isoquinoline (N₁), quinolizine (N₁), benzoxazine (N₁O₁),         benzodiazine (N₂), pyridopyridine (N₂), quinoxaline (N₂),         quinazoline (N₂), cinnoline (N₂), phthalazine (N₂),         naphthyridine (N2), pteridine (N₄);     -   C₁₁ (with 2 fused rings) derived from benzodiazepine (N₂);     -   C₁₃ (with 3 fused rings) derived from carbazole (N₁),         dibenzofuran (O₁), dibenzothiophene (S₁), carbolise (N₂),         pyrimidine (N₂), pyridoindole (N₂); and,     -   C₁₄ (with 3 fused rings) derived from acridine (N₁), xanthene         (O₁), thioxanthene (S₁), oxanthrene (O₂), phenoxathiin (O₁S₁),         phenazine (N₂), phenoxazine (N₁O₁), phenothiazine (N₁S₁),         thianthrene (S₂), phenanthridine (N₁), phenanthroline (N₂),         phenazine (N₂).

The above groups, whether alone or part of another substituent, may themselves optionally be substituted with one or more groups selected from themselves and the additional substituents listed below.

Halo: —F, —Cl, —Br, and

Hydroxy: —OH.

Ether: —OR, wherein R is an ether substituent, for example, a C₁₋₇ alkyl group (also referred to as a C₁₋₇ alkoxy group, discussed below), a C₃₋₂₀ heterocyclyl group (also referred to as a C₃₋₂₀ heterocyclyloxy group), or a C₅₋₂₀ aryl group (also referred to as a C₅₋₂₀ aryloxy group), preferably a C₁₋₇alkylgroup.

Alkoxy: —OR, wherein R is an alkyl group, for example, a C,₁₋₇ alkyl group. Examples of C₁₋₇ alkoxy groups include, but are not limited to, —OMe (methoxy), —OEt (ethoxy), —O(nPr) (n-propoxy), —O(iPr) (isopropoxy), —O(nBu) (n-butoxy), —O(sBu) (sec-butoxy), —O(iBu) (isobutoxy), and —O(tBu) (tert-butoxy).

Acetal: —CH(OR¹)(OR²), wherein R¹ and R² are independently acetal substituents, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group, or, in the case of a “cyclic” acetal group, R¹ and R², taken together with the two oxygen atoms to which they are attached, and the carbon atoms to which they are attached, form a heterocyclic ring having from 4 to 8 ring atoms. Examples of acetal groups include, but are not limited to, —CH(OMe)₂, —CH(OEt)₂, and —CH(OMe)(OEt).

Hemiacetal: —CH(OH)(OR¹), wherein R¹ is a hemiacetal substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of hemiacetal groups include, but are not limited to, —CH(OH)(OMe) and —CH(OH)(OEt),

Ketal: —CR(OR¹)(OR²), where R¹ and R² are as defined for acetals, and R is a ketal substituent other than hydrogen, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇alkyl group. Examples ketal groups include, but are not limited to, —C(Me)(OMe)₂, —C(Me)(OEt)₂, —C(Me)(OMe)(OEt), —C(Et)(OMe)₂, —C(Et)(OEt)₂, and —C(Et)(OMe)(OEt).

Hemiketal: —CR(OH)(OR¹), where R¹ is as defined for hemiacetals, and R is a hemiketal substituent other than hydrogen, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of hemiacetal groups include, but are not limited to, —C(Me)(OH)(OMe), —C(Et)(OH)(OMe), —C(Me)(OH)(OEt), and —C(Et)(OH)(OEt).

Oxo (keto, -one): ═O.

Thione (thioketone): ═S.

Imino (imine): ═NR, wherein R is an imino substituent, for example, hydrogen, C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably hydrogen or a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, ═NH, ═NMe, ═NEt, and ═NPh.

Formyl (carbaldehyde, carboxaldehyde): —C(═O)H,

Acyl (keto): —C(═O)R, wherein R is an acyl substituent, for example, a C₁₋₇ alkyl group (also referred to as C₁₋₇ alkylacyl or C₁₋₇ alkanoyl), a C₃₋₂₀ heterocyclylgroup (also referred to as C₃₋₂₀ heterocyclylacyl), or a C₅₋₂₀ aryl group (also referred to as C₅₋₂₀arylacyl), preferably a C₁₋₇ alkyl group. Examples of acyl groups include, but are not limited to, —C(═O)CH₃ (acetyl), —C(═O)CH₂CH₃ (propionyl), —C(═O)C(CH₃)₃ (t-butyryl), and —C(═O)Ph (benzoyl, phenone).

Carboxy (carboxylic acid): —C(═O)OH.

Thiocarboxy (thiocarboxylic acid): —C(═S)SH.

Thiolocarboxy (thiolocarboxylic acid): —C(═O)SH.

Thionocarboxy (thionocarboxylic acid): —C(═S)OH.

Imidic acid: —C(═NH)OH.

Hydroxamic acid: —C(═NOH)OH.

Ester (carboxylate, carboxylic acid ester, oxycarbonyl): —C(═O)OR, wherein R is an ester substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, —C(═O)OCH₃, —C(═O)OCH₂CH₃, —C(═O)OC(CH₃)₃, and —C(═O)OPh.

Acyloxy (reverse ester): —OC(═O)R, wherein R is an acyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of acyloxy groups include, but are not limited to, —OC(═O)CH₃ (acetoxy), —OC(═O)CH₂CH₃, —OC(═O)C(CH₃)₃, —OC(═O)Ph, and —OC(═O)CH₂Ph.

Oxycarboyloxy: —OC(═O)OR, wherein R is an ester substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, —OC(═O)OCH₃, —OC(═O)OCH₂CH₃, —OC(═O)OC(CH₃)₃, and —OC(═O)OPh.

Amino: —NR¹R², wherein R¹ and R² are independently amino substituents, for example, hydrogen, a alkyl group (also referred to as C₁₋₇ alkylamino or di-C₁₋₇ alkylamino), a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably H or a C₁₋₇ alkyl group, or, in the case of a “cyclic” amino group, R¹ and R², taken together with the nitrogen atom to which they are attached, form a heterocyclic ring having from 4 to 8 ring atoms. Amino groups may be primary (—NH₂), secondary (—NHR¹), or tertiary (—NHR¹R²), and in cationic form, may be quaternary (—⁺NR¹R²R³). Examples of amino groups include, but are not limited to, —NH₂, —NHCH₃, —NHC(CH₃)₂, —N(CH₃)₂, —N(CH₂CH₃)₂, and —NHPh. Examples of cyclic amino groups include, but are not limited to, aziridino, azetidino, pyrrolidino, piperidino, piperazino, morpholino, and thiomorpholino.

Amido (carbamoyl, carbamyl, aminocarbonyl, carboxamide): —C(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of amido groups include, but are not limited to, —C(═O)NH₂, —C(═O)NHCH₃, —C(═O)N(CH₃)₂, —C(═O)NHCH₂CH₃, and —C(═O)N(CH₂CH₃)₂, as well as amido groups in which R¹ and R², together with the nitrogen atom to which they are attached, form a heterocyclic structure as in, for example, piperidinocarbonyl, morpholinocarbonyl, thiomorpholinocarbonyl, and piperazinocarbonyl.

Thioamido (thiocarbamyl): —C(═S)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of amido groups include, but are not limited to, —C(═S)NH₂, —C(═S)NHCH₃, —C(═S)N(CH₃)₂, and —C(═S)NHCH₂CH₃.

Acylamido (acylamino): —NR¹C(═O)R², wherein R¹ is an amide substituent, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably hydrogen or a C₁₋₇ alkyl group, and R² is an acyl substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀aryl group, preferably hydrogen or a C₁₋₇ alkyl group. Examples of acylamide groups include, but are not limited to, —NHC(═O)CH₃, —NHC(═O)CH₂CH₃, and —NHC(═O)Ph. R¹ and R² may together form a cyclic structure, as in, for example, succinimidyl, maleimidyl, and phthalimidyl:

Aminocarbonyloxy: —OC(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of aminocarbonyloxy groups include, but are not limited to, —OC(═O)NH₂, —OC(═O)NHMe, —OC(═O)NMe₂, and —OC(═O)NEt₂.

Ureido: —N(R¹)CONR²R³ wherein R² and R³ are independently amino substituents, as defined for amino groups, and R¹ is a ureido substituent, for example, hydrogen, a C₁₋₇alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably hydrogen or a C₁₋₇ alkyl group. Examples of ureido groups include, but are not limited to, —NHCONH₂, —NHCONHMe, —NHCONHEt, —NHCONMe₂, —NHCONEt₂, —NMeCONH₂, —NMeCONHMe, —NMeCONHEt, —NMeCONMe₂, and —NMeCONEt₂.

Guanidino: —NH—C(═NH)NH₂.

Tetrazolyl: a five membered aromatic ring having four nitrogen atoms and one carbon atom,

Imino: ═NR, wherein R is an imino substituent, for example, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably H or a C₁₋₇alkyl group. Examples of imino groups include, but are not limited to, ═NH, ═NMe, and ═NEt.

Amidine (amidino): —C(═NR)NR₂, wherein each R is an amidine substituent, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably H or a C₁₋₇ alkyl group. Examples of amidine groups include, but are not limited to, —C(═NH)NH₂, —C(═NH)NMe₂, and —C(=NMe)NMe₂.

Nitro: —NO₂.

Nitroso: —NO.

Azido: —N₃.

Cyano (nitrile, carbonitrile): —CN.

Isocyano: —NC,

Cyanato: —CCN.

Isocyanato: —NCO.

Thiocyano (thiocyanato): —SCN.

Isothiocyano (isothiocyanato): —NCS.

Sulfhydryl (thiol, mercapto): —SH.

Thioether (sulfide): —SR, wherein R is a thioether substituent, for example, a C₁₋₇ alkyl group (also referred to as a C₁₋₇alkylthio group), a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of C₁₋₇alkylthio groups include, but are not limited to, —SCH₃ and —SCH₂CH₃.

Disulfide: —SS—R, wherein R is a disulfide substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group (also referred to herein as C₁₋₇ alkyl disulfide). Examples of C₁₋₇ alkyl disulfide groups include, but are not limited to, —SSCH₃ and —SSCH₂CH₃.

Sulfine (suffinyl, sulfoxide): —S(═O)R, wherein R is a sulfine substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfine groups include, but are not limited to, —S(═O)CH₃ and —S(═O)CH₂CH₃.

Sulfone (sulfonyl): —S(═O)₂R, wherein R is a sulfone substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group, including, for example, a fluorinated or perfluorinated C₁₋₇ alkyl group. Examples of sulfone groups include, but are not limited to, —S(═O)₂CH₃ (methanesulfonyl, mesyl), —S(═O)₂CF₃ (triflyl), —S(═O)₂CH₂CH₃ (esyl), —S(═O)₂C₄F₉ (nonaflyl), —S(═O)₂CH₂CF₃ (tresyl), —S(═O)₂CH₂CH₂NH₂ (tauryl), —S(═O)₂Ph (phenylsulfonyl, besyl), 4-methylphenylsulfonyl (tosyl), 4-chlorophenylsulfonyl (closyl), 4-bromophenylsuffonyl (brosyl), 4-nitrophenyl (nosyl), 2-naphthalenesulfonate (napsyl), and 5-dimethylamino-naphthalen-1-ylsulfonate (dansyl).

Sulfinic acid (sulfino): —S(═O)OH, —SO₂H.

Sulfonic acid (sulfo): —S(═O)₂OH, —SO₃H.

Sulfinate (sulfinic acid ester): —S(═O)OR; wherein R is a sulfinate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfinate groups include, but are not limited to, —S(═O)OCH₃ (methoxysulfinyl; methyl sulfinate) and —S(═O)OCH₂CH₃ (ethoxysulfinyl; ethyl sulfinate).

Sulfonate (sulfonic acid ester): —S(═O)₂OR, wherein R is a sulfonate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonate groups include, but are not limited to, —S(═O)₂OCH₃ (methoxysulfonyl; methyl sulfonate) and —S(═O)₂OCH₂CH₃ (ethoxysulfonyl; ethyl sulfonate).

Sulfinyloxy: —OS(═O)R, wherein R is a sulfinyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfinyloxy groups include, but are not limited to, —OS(═O)CH₃ and —OS(═O)CH₂CH₃.

Sulfonyloxy: —OS(═O)₂R, wherein R is a sulfonyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonyloxy groups include, but are not limited to, —OS(═O)₂CH₃ (mesylate) and —OS(═O)₂CH₂CH₃ (esylate).

Sulfate: —OS(═O)₂OR; wherein R is a sulfate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfate groups include, but are not limited to, —OS(═O)₂OCH₃ and —SO(═O)₂OCH₂CH₃.

Sulfamyl (sulfamoyl; sulfinic acid amide; sulfinamide): —S(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of sulfamyl groups include, but are not limited to, —S(═O)NH₂, —S(═O)NH(CH₃), —S(═O)N(CH₃)₂, —S(═O)NH(CH₂CH₃), —S(═O)N(CH₂CH₃)₂, and —S(═O)NHPh.

Sulfonamido (sulfinamoyl; sulfonic acid amide; sulfonamide): —S(═O)₂NR′R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of sulfonamido groups include, but are not limited to, —S(═O)₂NH₂, —S(═O)₂NH(CH₃), —S(═O)₂N(CH₃)₂, —S(═O)₂NH(CH₂CH₃), —S(═O)₂N(CH₂CH₃)₂, and —S(═O)₂NHPh.

Sulfamino: —NR¹S(═O)₂OH, wherein R¹ is an amino substituent, as defined for amino groups. Examples of sulfamino groups include, but are not limited to, —NHS(═O)₂OH and —N(CH₃)S(═O)₂OH.

Sulfonamino: —NR¹S(═O)₂R, wherein R¹ is an amino substituent, as defined for amino groups, and R is a sulfonamino substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀, aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonamino groups include, but are not limited to, —NHS(═O)₂CH₃ and —N(CH₃)S(═O)₂C₆H₅.

Sulfinamino: —NR¹S(═O)R, wherein R¹ is an amino substituent, as defined for amino groups, and R is a sulfinamino substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfinamino groups include, but are not limited to, —NHS(═O)CH₃ and —N(CH₃)S(═O)C₆H₅.

Phosphino (phosphine): —PR₂, wherein R is a phosphino substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphino groups include, but are not limited to, —PH₂, —P(CH₃)₂, —P(CH₂CH₃)₂, —P(t-Bu)₂, and —P(Ph)₂.

Phospho: —P(═O)₂.

Phosphinyl (phosphine oxide): —P(═O)R₂, wherein R is a phosphinyl substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group or a C₅₋₂₀ aryl group. Examples of phosphinyl groups include, but are not limited to, —P(═O)(CH₃)₂, —P(═O)(CH₂CH₃)₂, —P(═O)(t-Bu)₂, and —P(═O)(Ph)₂.

Phosphonic acid (phosphono): —P(═O)(OH)₂.

Phosphonate (phosphono ester): —P(═O)(OR)₂, where R is a phosphonate substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphonate groups include, but are not limited to, —P(═O)(OCH₃)₂, —P(═O)(OCH₂CH₃)₂, —P(═O)(O-t-Bu)₂, and —P(═O)(OPh)₂.

Phosphoric acid (phosphonooxy): —OP(═O)(OH)₂.

Phosphate (phosphonooxy ester): —OP(═O)(OR)₂, where R is a phosphate substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphate groups include, but are not limited to, —OP(═O)(OCH₃)₂, —OP(═O)(OCH₂CH₃)₂, —OP(═O)(O-t-Bu)₂, and —OP(═O)(OPh)₂.

Phosphorous acid: —OP(OH)₂.

Phosphite: —OP(OR)₂, where R is a phosphite substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphite groups include, but are not limited to, —OP(OCH₃)₂, —OP(OCH₂CH₃)₂, —OP(O-t-Bu)₂, and —OP(OPh)₂.

Phosphoramidite: —OP(OR¹)—NR² ₂, where R¹ and R² are phosphoramidite substituents, for example, —H, a (optionally substituted) C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphoramidite groups include, but are not limited to, —OP(OCH₂CH₃)—N(CH₃)₂, —OP(OCH₂CH₃)—N(i-Pr)₂, and —OP(OCH₂CH₂CN)—N(i-Pr)₂.

Phosphoramidate: —OP(═O)(OR)—NR² ₂, where R¹ and R² are phosphoramidate substituents, for example, —H, a (optionally substituted) C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphoramidate groups include, but are not limited to, —OP(═O)(OCH₂CH₃)—N(CH₃)₂, —OP(═O)(OCH₂CH₃)—N(i-Pr)₂, and —OP(═O)(OCH₂CH₂CN)—N(i-Pr)₂.

Alkylene

C₃₋₁₂ alkylene: The term “C₃₋₁₂ alkylene”, as used herein, pertains to a bidentate moiety obtained by removing two hydrogen atoms, either both from the same carbon atom, or one from each of two different carbon atoms, of a hydrocarbon compound having from 3 to 12 carbon atoms (unless otherwise specified), which may be aliphatic or alicyclic, and which may be saturated, partially unsaturated, or fully unsaturated. Thus, the term “alkylene” includes the sub-classes alkenylene, alkynylene, cycloalkylene, etc., discussed below.

Examples of linear saturated C₃₋₁₂ alkylene groups include, but are not limited to, —(CH₂)_(n)— where n is an integer from 3 to 12, for example, —CH₂CH₂CH₂— (propylene), —CH₂CH₂CH₂CH₂— (butylene), —CH₂CH₂CH₂CH₂CH₂— (pentylene) and —CH₂CH₂CH₂CH—₂CH₂CH₂CH₂— (heptylene).

Examples of branched saturated C₃₋₁₂ alkylene groups include, but are not limited to, —CH(CH₃)CH₂—, —CH(CH₃)CH₂CH₂—, —CH(CH₃)CH₂CH₂CH₂—, —CH₂CH(CH₃)CH₂—, —CH₂CH(CH₃)CH₂CH₂—, —CH(CH₂CH₃)—, —CH(CH₂CH₃)CH₂—, and —CH₂CH(CH₂CH₃)CH₂—.

Examples of linear partially unsaturated C₃₋₁₂ alkylene groups (C₃₋₁₂ alkenylene, and alkynylene groups) include, but are not limited to, —CH═CH—CH₂—, —CH₂—CH═CH₂—, —CH═CH—CH₂—CH₂—, —CH═CH—CH₂—CH₂—CH₂—, —CH═CH—CH═CH—, —CH═CH—CH═CH—CH₂—, —CH═CH—CH═CH—CH₂—CH₂—, —CH═CH—CH₂—CH═CH—, —CH═CH—CH₂—CH₂—CH═CH—, and —CH₂—C≡C—CH₂—.

Examples of branched partially unsaturated C₃₋₁₂ alkylene groups (C₃₋₁₂ alkenylene and alkynylene groups) include, but are not limited to, —C(CH₃)═CH—, —C(CH₃)═CH—CH₂—, —CH═CH—CH(CH₃)— and —C≡C—CH(CH₃)—.

Examples of alicyclic saturated C₃₋₁₂ alkylene groups (C₃₋₁₂ cycloalkylenes) include, but are not limited to, cyclopentylene (e.g. cyclopent-1,3-ylene), and cyclohexylene (e.g. cyclohex-1,4-ylene).

Examples of alicyclic partially unsaturated C₃₋₁₂ alkylene groups (C₃₋₁₂ cycloalkylenes) include, but are not limited to, cyclopentenylene (e.g. 4-cyclopenten-1,3-ylene), cyclohexenylene (e.g. 2-cyclohexen-1,4-ylene; 3-cyclohexen-1,2-ylene; 2,5-cyclohexadien-1,4-ylene).

Oxygen protecting group: the term “oxygen protecting group” refers to a moiety which masks a hydroxy group, and these are well known in the art. A large number of suitable groups are described on pages 23 to 200 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference. Classes of particular interest include silyl ethers (e.g. TMS, TBDMS), substituted methyl ethers (e.g. THP) and esters (e.g. acetate).

Carbarnate nitrogen protecting group: the term “carbamate nitrogen protecting group” pertains to a moiety which masks the nitrogen in the imine bond, and these are well known in the art. These groups have the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 503 to 549 of Greene, T. W, and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

Hemi-aminal nitrogen protecting group: the term “hemi-aminal nitrogen protecting group” pertains to a group having the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 633 to 647 as amide protecting groups of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides Conjugates comprising a PBD dimer connected to a Ligand unit via a Linker Unit. In one embodiment, the Linker unit includes a Stretcher unit (A), a Specificity unit (L¹), and a Spacer unit (L²). The Linker unit is connected at one end to the Ligand unit and at the other end to the PBD dimer compound.

In one aspect, such a Conjugate is shown below in formula Ia:

L-(A¹ _(a)-L¹ _(s)-L² _(y)-D)_(p)   (Ia)

-   -   wherein:     -   L is the Ligand unit; and     -   -A¹ _(a)-L¹ _(s)-L² _(y)- is a Linker unit (LU), wherein:     -   -A¹- is a Stretcher unit,     -   a is 1 or 2,     -   L¹- is a Specificity unit,     -   s is an integer ranging from 1 to 12,     -   -L²- is a Spacer unit,     -   y is 0, 1 or 2;     -   -D is an PBD dimer; and     -   p is from 1 to 20.

The drug loading is represented by p, the number of drug molecules per Ligand unit (e.g., an antibody). Drug loading may range from 1 to 20 Drug units (D) per Ligand unit (e.g., Ab or mAb). For compositions, p represents the average drug loading of the Conjugates in the composition, and p ranges from 1 to 20.

In some embodiments, p is from about 1 to about 8 Drug units per Ligand unit. In some embodiments, p is 1. In some embodiments, p is 2. In some embodiments, p is from about 2 to about 8 Drug units per Ligand unit. In some embodiments, p is from about 2 to about 6, 2 to about 5, or 2 to about 4 Drug units per Ligand unit. In some embodiments, p is about 2, about 4, about 6 or about 8 Drug units per Ligand unit.

The average number of Drugs units per Ligand unit in a preparation from a conjugation reaction may be characterized by conventional means such as mass spectroscopy, ELISA assay, and HPLC. The quantitative distribution of Conjugates in terms of p may also be determined. In some instances, separation, purification, and characterization of homogeneous Conjugates, where p is a certain value, from Conjugates with other drug loadings may be achieved by means such as reverse phase HPLC or electrophoresis.

In another aspect, such a Conjugate is shown below in formula Ib:

-   -   Also illustrated as:

L-(A¹ _(a)-L² _(y)(-L¹ _(s))-D)_(p)   (Ib)

-   -   wherein:     -   L is the Ligand unit; and     -   -A¹ ₂-L¹ _(s)(L² _(y))- is a Linker unit (LU), wherein:     -   -A¹- is a Stretcher unit linked to a Stretcher unit (L²),     -   a is 1 or 2,     -   L¹- is a Specificity unit linked to a Stretcher unit (L²),     -   s is an integer ranging from 0 to 12,     -   -L²- is a Spacer unit,     -   y is 0, 1 or 2;     -   -D is a PBD dimer; and     -   p is from 1 to 20,

Preferences

The following preferences may apply to all aspects of the invention as described above, or may relate to a single aspect. The preferences may be combined together in any combination.

In one embodiment, the Conjugate has the formula:

L-(A¹ _(a)-L¹ _(s)-L² _(y)-D)_(p)

wherein L, A¹, a, L¹, s, L², D and p are as described above.

In one embodiment, the Ligand unit (L) is a Cell Binding Agent (CBA) that specifically binds to a target molecule on the surface of a target cell. An exemplary formula is illustrated below:

-   -   where the asterisk indicates the point of attachment to the Drug         unit (D), CBA is the Cell Binding Agent, L¹ is a Specificity         unit, A¹ is a Stretcher unit connecting L¹ to the Cell Binding         Agent, L² is a Spacer unit, which is a covalent bond, a         self-immolative group or together with —OC(═O)— forms a         self-immolative group, and L² optional.

In another embodiment, the Ligand unit (L) is a Cell Binding Agent (CBA) that specifically binds to a target molecule on the surface of a target cell. An exemplary formula is illustrated below:

CBA-A¹ _(a)-L¹ _(s)-L² _(y)-*

-   -   where the asterisk indicates the point of attachment to the Drug         unit (D), CBA is the Cell Binding Agent, L¹ is a Specificity         unit, A¹ is a Stretcher unit connecting L¹ to the Cell Binding         Agent, L² is a Spacer unit which is a covalent bond or a         self-immolative group, and a is 1 or 2, s is 0, 1 or 2, and y is         0 or 1 or 2.

In the embodiments illustrated above, L¹ can be a cleavable Specificity unit, and may be referred to as a “trigger” that when cleaved activates a self-immolative group (or self-immolative groups) L², when a self-immolative group(s) is present. When the Specificity unit L¹ is cleaved, or the linkage (i.e., the covalent bond) between L¹ and L² is cleaved, the self-immolative group releases the Drug unit (D).

In another embodiment, the Ligand unit (L) is a Cell Binding Agent (CBA) that specifically binds to a target molecule on the surface of a target cell. An exemplary formula is illustrated below:

-   -   where the asterisk indicates the point of attachment to the Drug         (D), CBA is the Cell Binding Agent, L¹ is a Specificity unit         connected to L², A¹ is a Stretcher unit connecting L² to the         Cell Binding Agent, L² is a self-immolative group, and a is 1 or         2, s is 1 or 2, and y is 1 or 2.

In the various embodiments discussed herein, the nature of L¹ and L² can vary widely. These groups are chosen on the basis of their characteristics, which may be dictated in part, by the conditions at the site to which the conjugate is delivered. Where the Specificity unit L¹ is cleavable, the structure and/or sequence of L¹ is selected such that it is cleaved by the action of enzymes present at the target site (e.g., the target cell). L¹ units that are cleavable by changes in pH (e.g. acid or base labile), temperature or upon irradiation (e.g. photolabile) may also be used. L¹ units that are cleavable under reducing or oxidising conditions may also find use in the Conjugates.

In some embodiments, L¹ may comprise one amino acid or a contiguous sequence of amino acids. The amino acid sequence may be the target substrate for an enzyme.

In one embodiment, L¹ is cleavable by the action of an enzyme. In one embodiment, the enzyme is an esterase or a peptidase. For example, L¹ may be cleaved by a lysosomal protease, such as a cathepsin.

In one embodiment, L² is present and together with —C(═O)O— forms a self-immolative group or self-immolative groups. In some embodiments, —C(═O)O— also is a self-immolative group.

In one embodiment, where L¹ is cleavable by the action of an enzyme and L² is present, the enzyme cleaves the bond between L¹ and L², whereby the self-immolative group(s) release the Drug unit.

L¹ and L², where present, may be connected by a bond selected from:

-   -   —C(═O)NH—,     -   —C(═O)O—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OC(═O)O—,     -   —NHC(═O)O—,     -   —OC(═O)NH—,     -   —NHC(═O)NH, and     -   —O— (a glycosidic bond).

An amino group of L¹ that connects to L² may be the N-terminus of an amino acid or may be derived from an amino group of an amino acid side chain, for example a lysine amino acid side chain.

A carboxyl group of L¹ that connects to L² may be the C-terminus of an amino acid or may be derived from a carboxyl group of an amino acid side chain, for example a glutamic acid amino acid side chain.

A hydroxy group of L¹ that connects to L² may be derived from a hydroxy group of an amino acid side chain, for example a serine amino acid side chain.

In one embodiment, —C(═O)O— and L² together form the group:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, the wavy line indicates the point of attachment to the L¹,         Y is —N(H)—, —O—, —C(═O)N(H)— or —C(═O)O—, and n is 0 to 3. The         phenylene ring is optionally substituted with one, two or three         substituents as described herein.

In one embodiment, Y is NH.

In one embodiment, n is 0 or 1. Preferably, n is 0.

Where Y is NH and n is 0, the self-immolative group may be referred to as a p-aminobenzylcarbonyl linker (PABC).

The self-immolative group will allow for release of the Drug unit (i.e., the asymmetric PBD) when a remote site in the linker is activated, proceeding along the lines shown below (for n=0):

-   -   where the asterisk indicates the attachment to the Drug, L* is         the activated form of the remaining portion of the linker and         the released Drug unit is not shown. These groups have the         advantage of separating the site of activation from the Drug.

In another embodiment, —C(═O)O— and L² together form a group selected from:

-   -   where the asterisk, the wavy line, Y, and n are as defined         above. Each phenylene ring is optionally substituted with one,         two or three substituents as described herein. In one         embodiment, the phenylene ring having the Y substituent is         optionally substituted and the phenylene ring not having the Y         substituent is unsubstituted.

In another embodiment, —C(═O)O— and L² together form a group selected from:

-   -   where the asterisk, the wavy line, Y, and n are as defined         above, E is O, S or NR, D is N, CH, or CR, and F is N, CH, or         CR.

In one embodiment, D is N.

In one embodiment, D is CH.

In one embodiment, E is O or S.

In one embodiment, F is CH.

In a preferred embodiment, the covalent bond between L¹ and L² is a cathepsin labile (e.g., cleavable) bond.

In one embodiment, L¹ comprises a dipeptide. The amino acids in the dipeptide may be any combination of natural amino acids and non-natural amino acids. In some embodiments, the dipeptide comprises natural amino acids. Where the linker is a cathepsin labile linker, the dipeptide is the site of action for cathepsin-mediated cleavage. The dipeptide then is a recognition site for cathepsin.

In one embodiment, the group —X₁-X₂— in dipeptide, —NH—X₁-X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-,     -   -Val-Cit-,     -   -Phe-Cit-,     -   -Leu-Cit-,     -   -Ile-Cit-,     -   -Phe-Arg-, and     -   -Trp-Cit-;

where Cit is citrulline. In such a dipeptide, —NH— is the amino group of X₁, and CO is the carbonyl group of X₂.

Preferably, the group —X₁-X₂— in dipeptide, —NH—X₁-X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-, and     -   -Val-Cit-.

Most preferably, the group —X₁-X₂— in dipeptide, —NH—X₁-X₂—CO—, is -Phe-Lys-, Val-Cit or -Val-Ala-.

Other dipeptide combinations of interest include:

-   -   -Gly-Gly-,     -   -Pro-Pro-, and     -   -Val-Glu-.

Other dipeptide combinations may be used, including those described by Dubowchik et al., which is incorporated herein by reference.

In one embodiment, the amino acid side chain is chemically protected, where appropriate. The side chain protecting group may be a group as discussed below. Protected amino acid sequences are cleavable by enzymes. For example, a dipeptide sequence comprising a Boc side chain-protected Lys residue is cleavable by cathepsin.

Protecting groups for the side chains of amino acids are well known in the art and are described in the Novabiochem Catalog. Additional protecting group strategies are set out in Protective groups in Organic Synthesis, Greene and Wuts.

Possible side chain protecting groups are shown below for those amino acids having reactive side chain functionality:

-   -   Arg: Z, Mtr, Tos;     -   Asn: Trt, Xan;     -   Asp: Bzl, t-Bu;     -   Cys: Acm, Bzl, Bzl-OMe, Bzl-Me, Trt;     -   Glu: Bzl, t-Bu;     -   Gln: Trt, Xan;     -   His: Boc, Dnp, Tos, Trt;     -   Lys: Boc, Z—Cl, Fmoc, Z;     -   Ser: Bzl, TBDMS, TBDPS;     -   Thr: Bz;     -   Trp: Boc;     -   Tyr: Bzl, Z, Z—Br.

In one embodiment, —X₂— is connected indirectly to the Drug unit. In such an embodiment, the Spacer unit L² is present.

In one embodiment, the dipeptide is used in combination with a self-immolative group(s) (the Spacer unit). The self-immolative group(s) may be connected to —X₂—.

Where a self-immolative group is present, —X₂— is connected directly to the self-immolative group. In one embodiment, —X₂— is connected to the group Y of the self-immolative group. Preferably the group —X₂—CO— is connected to Y, where Y is NH.

—X₁— is connected directly to A¹. In one embodiment, —X₁— is connected directly to A¹. Preferably the group NH—X₁— (the amino terminus of X₁) is connected to A¹. A¹ may comprise the functionality —CO— thereby to form an amide link with —X₁—.

In one embodiment, L¹ and L² together with —OC(═O)— comprise the group —X₁-X₂-PABC-. The PABC group is connected directly to the Drug unit. In one example, the self-immolative group and the dipeptide together form the group -Phe-Lys-PABC-, which is illustrated below:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, and the wavy line indicates the point of attachment to the         remaining portion of L¹ or the point of attachment to A¹.         Preferably, the wavy line indicates the point of attachment to         A¹.

Alternatively, the self-immolative group and the dipeptide together form the group Nal-Ala-PABC-, which is illustrated below:

-   -   where the asterisk and the wavy line are as defined above.

In another embodiment, L¹ and L² together with —OC(═O)— represent:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, the wavy line indicates the point of attachment to A¹, Y         is a covalent bond or a functional group, and E is a group that         is susceptible to cleavage thereby to activate a self-immolative         group.

E is selected such that the group is susceptible to cleavage, e.g., by light or by the action of an enzyme. E may be —NO₂ or glucuronic acid (e.g., ii-glucuronic acid). The former may be susceptible to the action of a nitroreductase, the latter to the action of a β-glucuronidase.

The group Y may be a covalent bond.

The group Y may be a functional group selected from:

-   -   —C(═O)—     -   —NH—     -   —O—     -   —C(═O)NH—,     -   —C(═O)O—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OC(═O)O—,     -   —NHC(═O)O—,     -   —OC(═O)NH—,     -   —NHC(═O)NH—,     -   —NHC(═O)NH,     -   —C(═O)NHC(═O)—,     -   SO₂, and     -   —S—.

The group Y is preferably —NH—, —CH₂—, —O—, and —S—.

In some embodiments, L¹ and L² together with —OC(═O)— represent:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, the wavy line indicates the point of attachment to A, Y is         a covalent bond or a functional group and E is glucuronic acid         (e.g., β-glucuronic acid). Y is preferably a functional group         selected from —NH—.

In some embodiments, L¹ and L² together represent:

-   -   where the asterisk indicates the point of attachment to the         remainder of L² or the Drug unit, the wavy line indicates the         point of attachment to A¹, Y is a covalent bond or a functional         group and E is glucuronic acid (e.g., β-glucuronic acid). Y is         preferably a functional group selected from —NH—, —CH₂—, —O—,         and —S—.

In some further embodiments, Y is a functional group as set forth above, the functional group is linked to an amino acid, and the amino acid is linked to the Stretcher unit A¹. In some embodiments, amino acid is β-alanine. In such an embodiment, the amino acid is equivalently considered part of the Stretcher unit.

The Specificity unit L¹ and the Ligand unit are indirectly connected via the Stretcher unit.

L¹ and A¹ may be connected by a bond selected from:

-   -   —C(═O)NH—,     -   —C(═O)O—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OC(═O)O—,     -   —NHC(═O)O—,     -   —OC(═O)NH—, and     -   —NHC(═O)NH—.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the connection between the Ligand unit and A¹ is through a thiol residue of the Ligand unit and a maleimide group of A¹.

In one embodiment, the connection between the Ligand unit and A¹ is:

-   -   where the asterisk indicates the point of attachment to the         remaining portion of A¹, L¹, L² or D, and the wavy line         indicates the point of attachment to the remaining portion of         the Ligand unit. In this embodiment, the S atom is typically         derived from the Ligand unit.

In each of the embodiments above, an alternative functionality may be used in place of the malemide-derived group shown below:

-   -   where the wavy line indicates the point of attachment to the         Ligand unit as before, and the asterisk indicates the bond to         the remaining portion of the A¹ group, or to L¹, L² or D.

In one embodiment, the maleimide-derived group is replaced with the group:

-   -   where the wavy line indicates point of attachment to the Ligand         unit, and the asterisk indicates the bond to the remaining         portion of the A¹ group or to L¹, L² or D.

In one embodiment, the maleimide-derived group is replaced with a group, which optionally together with a Ligand unit (e.g., a Cell Binding Agent), is selected from:

-   -   —C(═O)NH—,     -   —C(═O)O—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OC(═O)O—,     -   —NHC(═O)O—,     -   —OC(═O)NH—,     -   —NHC(═O)NH—,     -   —NHC(═O)NH,     -   —C(═O)NHC(═O)—,     -   —S—,     -   —S—S—,     -   —CH₂C(═O)—     -   —C(═O)CH₂—,     -   ═N—NH—, and     -   —NH—N═.

In one embodiment, the maleimide-derived group is replaced with a group, which optionally together with the Ligand unit, is selected from:

-   -   where the wavy line indicates either the point of attachment to         the Ligand unit or the bond to the remaining portion of the A¹         group, and the asterisk indicates the other of the point of         attachment to the Ligand unit or the bond to the remaining         portion of the A¹ group.

Other groups suitable for connecting L¹ to the Cell Binding Agent are described in WO 2005/082023.

In one embodiment, the Stretcher unit A¹ is present, the Specificity unit L¹ is present and Spacer unit L² is absent. Thus, L¹ and the Drug unit are directly connected via a bond. Equivalently in this embodiment, L² is a bond.

L¹ and D may be connected by a bond selected from:

-   -   —C(═O)N H—,     -   —C(═O)—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OC(═O)O—,     -   —NHC(═)O—,     -   —OC(═O)NH—, and     -   —NHC(═O)NH—.

In one embodiment, L¹ and D are preferably connected by a bond selected from:

-   -   —C(═O)NH—, and     -   —NHC(═O)—.

In one embodiment, L¹ comprises a dipeptide and one end of the dipeptide is linked to D. As described above, the amino acids in the dipeptide may be any combination of natural amino acids and non-natural amino acids. In some embodiments, the dipeptide comprises natural amino acids. Where the linker is a cathepsin labile linker, the dipeptide is the site of action for cathepsin-mediated cleavage. The dipeptide then is a recognition site for cathepsin.

In one embodiment, the group —X₁-X₂— in dipeptide, —NH—X₁-X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-,     -   -Val-Cit-,     -   -Phe-Cit-,     -   -Leu-Cit-,     -   -Ile-Cit-,     -   -Phe-Arg-, and     -   -Trp-Cit-;

where Cit is citrulline. In such a dipeptide, —NH— is the amino group of X₁, and CO is the carbonyl group of X₂.

Preferably, the group —X₁-X₂— in dipeptide, —NH—X₁-X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-, and     -   -Val-Cit-.

Most preferably, the group —X₁-X₂— in dipeptide, —NH—X₁-X₂—CO—, is -Phe-Lys- or -Val-Ala-.

Other dipeptide combinations of interest include:

-   -   -Gly-Gy-,     -   -Pro-Pro-, and     -   -Val-Glu-.

Other dipeptide combinations may be used, including those described above.

In one embodiment, L¹-D is:

-   -   where —NH—X₁-X₂—CO is the dipeptide, —NH— is part of the Drug         unit, the asterisk indicates the point of attachment to the         remainder of the Drug unit, and the wavy line indicates the         point of attachment to the remaining portion of L¹ or the point         of attachment to A¹. Preferably, the wavy line indicates the         point of attachment to A¹.

In one embodiment, the dipeptide is valine-alanine and L¹-D is:

-   -   where the asterisk, —NH— and the wavy line are as defined above.

In one embodiment, the dipeptide is phenylalanine-lysine and L¹-D is:

-   -   where the asterisk, —NH— and the wavy line are as defined above.

In one embodiment, the dipeptide is valine-citrulline.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to D, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to D, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to D, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 7, preferably 3 to 7, most preferably 3         or 7.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L¹ or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 8, preferably 4 to 8, most         preferably 4 or 8.

In one embodiment, the groups A¹-L¹ is:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 8, preferably 4 to 8, most         preferably 4 or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to D, S is         a sulphur group of the Ligand unit, the wavy line indicates the         point of attachment to the rest of the Ligand unit, and n is 0         to 6. In one embodiment, n is 5.

In one embodiment, the group L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to D, S is         a sulphur group of the Ligand unit, the wavy line indicates the         point of attachment to the remainder of the Ligand unit, and n         is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to D, S is         a sulphur group of the Ligand unit, the wavy line indicates the         point of attachment to the remainder of the Ligand unit, n is 0         or 1, and in is 0 to 30. In a preferred embodiment, n is 1 and m         is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4 or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to 0, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 7, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, n is 0 or 1, and m is 0 to 30. In a         preferred embodiment, n is 1 and m is 0 to 10, 1 to 8,         preferably 4 to 8, most preferably 4 or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, n is 0 or 1, and m is 0 to 30. In a         preferred embodiment, n is 1 and m is 0 to 10, 1 to 8,         preferably 4 to 8, most preferably 4 or 8.

In one embodiment, the Stretcher unit is an acetamide unit, having the formula:

-   -   where the asterisk indicates the point of attachment to the         remainder of the Stretcher unit, L¹ or D, and the wavy line         indicates the point of attachment to the Ligand unit.

In other embodiments, Linker-Drug compounds are provided for conjugation to a Ligand unit. In one embodiment, the Linker-Drug compounds are designed for connection to a Cell Binding Agent.

In one embodiment, the Drug Linker compound has the formula:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, G¹ is a Stretcher group (A¹) to form a connection to a         Ligand unit, L¹ is a Specificity unit, L² (a Spacer unit) is a         covalent bond or together with —OC(═O)— forms a self-immolative         group(s).

In another embodiment, the Drug Linker compound has the formula:

G¹-L¹-L²-

-   -   where the asterisk indicates the point of attachment to the Drug         unit, G¹ is a Stretcher unit (A¹) to form a connection to a         Ligand unit, L¹ is a Specificity unit, L² (a Spacer unit) is a         covalent bond or a self-immolative group(s).

L¹ and L² are as defined above. References to connection to A¹ can be construed here as referring to a connection to G¹.

In one embodiment, where L¹ comprises an amino acid, the side chain of that amino acid may be protected. Any suitable protecting group may be used. In one embodiment, the side chain protecting groups are removable with other protecting groups in the compound, where present. In other embodiments, the protecting groups may be orthogonal to other protecting groups in the molecule, where present.

Suitable protecting groups for amino acid side chains include those groups described in the Novabiochem Catalog 2006/2007. Protecting groups for use in a cathepsin labile linker are also discussed in Dubowchik et al.

In certain embodiments of the invention, the group L¹ includes a Lys amino acid residue. The side chain of this amino acid may be protected with a Boc or Alloc protected group. A Boc protecting group is most preferred.

The functional group G¹ forms a connecting group upon reaction with a Ligand unit (e.g., a cell binding agent.

In one embodiment, the functional group G¹ is or comprises an amino, carboxylic acid, hydroxy, thiol, or maleimide group for reaction with an appropriate group on the Ligand unit. In a preferred embodiment, G¹ comprises a maleimide group.

In one embodiment, the group G¹ is an alkyl maleimide group. This group is suitable for reaction with thiol groups, particularly cysteine thiol groups, present in the cell binding agent, for example present in an antibody.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²or         D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²or         D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 2, preferably 4 to 8, and most preferably 4         or 8.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 8, preferably 4 to 8, and most preferably 4         or 8.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²         or D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²         or D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 2, preferably 4 to 8, and most preferably 4         or 8.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 8, preferably 4 to 8, and most preferably 4         or 8.

In each of the embodiments above, an alternative functionality may be used in place of the malemide group shown below:

-   -   where the asterisk indicates the bond to the remaining portion         of the G group.

In one embodiment, the maleimide-derived group is replaced with the group:

-   -   where the asterisk indicates the bond to the remaining portion         of the G group.

In one embodiment, the maleimide group is replaced with a group selected from:

-   -   —C(═O)OH,     -   —OH,     -   —NH₂,     -   —SH,     -   —C(═O)CH₂X, where X is Cl, Br or I,     -   —CHO,     -   —NHNH₂     -   —C≡CH, and     -   —N₃ (azide).

In one embodiment, L¹ is present, and G¹ is —NH₂, —NHMe, —COOH, —OH or —SH.

In one embodiment, where L¹ is present, G¹ is —NH₂ or —NHMe. Either group may be the N-terminal of an L¹ amino acid sequence.

In one embodiment, L¹ is present and G¹ is —NH₂, and L¹ is an amino acid sequence —X₁-X₂—, as defined above.

In one embodiment, L¹ is present and G¹ is COOH. This group may be the C-terminal of an L¹ amino acid sequence.

In one embodiment, L¹ is present and G¹ is OH.

In one embodiment, L¹ is present and G¹ is SH.

The group G¹ may be convertable from one functional group to another. In one embodiment, L¹ is present and G¹ is —NH₂. This group is convertable to another group G¹ comprising a maleimide group. For example, the group —NH₂ may be reacted with an acids or an activated acid (e.g., N-succinimide forms) of those G¹ groups comprising maleimide shown above.

The group G¹ may therefore be converted to a functional group that is more appropriate for reaction with a Ligand unit.

As noted above, in one embodiment, L¹ is present and G¹ is —NH₂, —NHMe, —COOH, —OH or —SH. In a further embodiment, these groups are provided in a chemically protected form. The chemically protected form is therefore a precursor to the linker that is provided with a functional group.

In one embodiment, G¹ is —NH₂ in a chemically protected form. The group may be protected with a carbamate protecting group. The carbamate protecting group may be selected from the group consisting of:

-   -   Alloc, Fmoc, Boc, Troc, Teoc, Cbz and PNZ.

Preferably, where G¹ is —NH₂, it is protected with an Alloc or Fmoc group.

In one embodiment, where G¹ is —NH₂, it is protected with an Fmoc group.

In one embodiment, the protecting group is the same as the carbamate protecting group of the capping group.

In one embodiment, the protecting group is not the same as the carbamate protecting group of the capping group. In this embodiment, it is preferred that the protecting group is removable under conditions that do not remove the carbamate protecting group of the capping group.

The chemical protecting group may be removed to provide a functional group to form a connection to a Ligand unit. Optionally, this functional group may then be converted to another functional group as described above.

In one embodiment, the active group is an amine. This amine is preferably the N-terminal amine of a peptide, and may be the N-terminal amine of the preferred dipeptides of the invention.

The active group may be reacted to yield the functional group that is intended to form a connection to a Ligand unit.

In other embodiments, the Linker unit is a precursor to the Linker unit having an active group. In this embodiment, the Linker unit comprises the active group, which is protected by way of a protecting group. The protecting group may be removed to provide the Linker unit having an active group.

Where the active group is an amine, the protecting group may be an amine protecting group, such as those described in Green and Wuts.

The protecting group is preferably orthogonal to other protecting groups, where present, in the Linker unit.

In one embodiment, the protecting group is orthogonal to the capping group. Thus, the active group protecting group is removable whilst retaining the capping group. In other embodiments, the protecting group and the capping group is removable under the same conditions as those used to remove the capping group.

In one embodiment, the Linker unit is:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, and the wavy line indicates the point of attachment to the         remaining portion of the Linker unit, as applicable or the point         of attachment to G¹. Preferably, the wavy line indicates the         point of attachment to G¹.

In one embodiment, the Linker unit is:

-   -   where the asterisk and the wavy line are as defined above.

Other functional groups suitable for use in forming a connection between L¹ and the Cell Binding Agent are described in WO 2005/082023.

Ligand Unit

The Ligand Unit may be of any kind, and include a protein, polypeptide, peptide and a non-peptidic agent that specifically binds to a target molecule. In some embodiments, the Ligand unit may be a protein, polypeptide or peptide. In some embodiments, the Ligand unit may be a cyclic polypeptide. These Ligand units can include antibodies or a fragment of an antibody that contains at least one target molecule-binding site, lymphokines, hormones, growth factors, or any other cell binding molecule or substance that can specifically bind to a target.

Examples of Ligand units include those agents described for use in WO 2007/085930, which is incorporated herein.

In some embodiments, the Ligand unit is a Cell Binding Agent that binds to an extracellular target on a cell. Such a Cell Binding Agent can be a protein, polypeptide, peptide or a non-peptidic agent. In some embodiments, the Cell Binding Agent may be a protein, polypeptide or peptide. In some embodiments, the Cell Binding Agent may be a cyclic polypeptide. The Cell Binding Agent also may be antibody or an antigen-binding fragment of an antibody. Thus, in one embodiment, the present invention provides an antibody-drug conjugate (ADC).

In one embodiment the antibody is a monoclonal antibody; chimeric antibody; humanized antibody; fully human antibody; or a single chain antibody. One embodiment the antibody is a fragment of one of these antibodies having biological activity. Examples of such fragments include Fab, Fab′, F(ab′)₂ and Fv fragments.

The antibody may be a diabody, a domain antibody (DAB) or a single chain antibody.

In one embodiment, the antibody is a monoclonal antibody.

Antibodies for use in the present invention include those antibodies described in WO 2005/082023 which is incorporated herein. Particularly preferred are those antibodies for tumour-associated antigens. Examples of those antigens known in the art include, but are not limited to, those tumour-associated antigens set out in WO 2005/082023. See, for instance, pages 41-55.

In some embodiments, the conjugates are designed to target tumour cells via their cell surface antigens. The antigens may be cell surface antigens which are either over-expressed or expressed at abnormal times or cell types. Preferably, the target antigen is expressed only on proliferative cells (preferably tumour cells); however this is rarely observed in practice. As a result, target antigens are usually selected on the basis of differential expression between proliferative and healthy tissue.

Antibodies have been raised to target specific tumour related antigens including:

-   -   Cripto, CD19, CD20, CD22, CD30, CD33, Glycoprotein NMB, CanAg,         Her2 (ErbB2/Neu), CD56 (NCAM), CD70, CD79, CD138, PSCA, PSMA         (prostate specific membrane antigen), BCMA, E-selectin, EphB2,         Melanotransferin, Muc16 and TMEFF2.

The Ligand unit is connected to the Linker unit. In one embodiment, the Ligand unit is connected to A, where present, of the Linker unit.

In one embodiment, the connection between the Ligand unit and the Linker unit is through a thioether bond.

In one embodiment, the connection between the Ligand unit and the Linker unit is through a disulfide bond.

In one embodiment, the connection between the Ligand unit and the Linker unit is through an amide bond.

In one embodiment, the connection between the Ligand unit and the Linker unit is through an ester bond.

In one embodiment, the connection between the Ligand unit and the Linker is formed between a thiol group of a cysteine residue of the Ligand unit and a maleimide group of the Linker unit.

The cysteine residues of the Ligand unit may be available for reaction with the functional group of the Linker unit to form a connection. In other embodiments, for example where the Ligand unit is an antibody, the thiol groups of the antibody may participate in interchain disulfide bonds. These interchain bonds may be converted to free thiol groups by e.g. treatment of the antibody with DTT prior to reaction with the functional group of the Linker unit.

In some embodiments, the cysteine residue is an introduced into the heavy or light chain of an antibody. Positions for cysteine insertion by substitution in antibody heavy or light chains include those described in Published U.S. Application No. 2007-0092940 and International Patent Publication WO2008070593, which are incorporated herein.

Methods of Treatment

The Conjugates of the present invention may be used in a method of therapy. Also provided is a method of treatment, comprising administering to a subject in need of treatment a therapeutically-effective amount of a Conjugate of formula I. The term “therapeutically effective amount” is an amount sufficient to show benefit to a patient. Such benefit may be at least amelioration of at least one symptom. The actual amount of a Conjugate administered, and rate and time-course of administration, will depend on the nature and severity of what is being treated. Prescription of treatment, e.g. decisions on dosage, is within the responsibility of general practitioners and other medical doctors.

In some embodiments, the amount of the Conjugate administered ranges from about 0.01 to about 10 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.01 to about 5 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.05 to about 5 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 5 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 4 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.05 to about 3 mg/kg per dose.

In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 3 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 2 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.01 to about 1 mg/kg per dose.

A conjugate may be administered alone or in combination with other treatments, either simultaneously or sequentially dependent upon the condition to be treated. Examples of treatments and therapies include, but are not limited to, chemotherapy (the administration of active agents, including, e.g. drugs; surgery; and radiation therapy).

Pharmaceutical compositions according to the present invention, and for use in accordance with the present invention, may comprise, in addition to the active ingredient, i.e. a Conjugate of formula I, a pharmaceutically acceptable excipient, carrier, buffer, stabiliser or other materials well known to those skilled in the art. Such materials should be non-toxic and should not interfere with the efficacy of the active ingredient. The precise nature of the carrier or other material will depend on the route of administration, which may be oral, or by injection, e.g. cutaneous, subcutaneous, or intravenous.

Pharmaceutical compositions for oral administration may be in tablet, capsule, powder or liquid form. A tablet may comprise a solid carrier or an adjuvant. Liquid pharmaceutical compositions generally comprise a liquid carrier such as water, petroleum, animal or vegetable oils, mineral oil or synthetic oil. Physiological saline solution, dextrose or other saccharide solution or glycols such as ethylene glycol, propylene glycol or polyethylene glycol may be included. A capsule may comprise a solid carrier such a gelatin,

For intravenous, cutaneous or subcutaneous injection, or injection at the site of affliction, the active ingredient will be in the form of a parenterally acceptable aqueous solution which is pyrogen-free and has suitable pH, isotonicity and stability. Those of relevant skill in the art are well able to prepare suitable solutions using, for example, isotonic vehicles such as Sodium Chloride Injection, Ringer's Injection, Lactated Ringer's Injection. Preservatives, stabilisers, buffers, antioxidants and/or other additives may be included, as required,

Includes Other Forms

Unless otherwise specified, included in the above are the well known ionic, salt, solvate, and protected forms of these substituents. For example, a reference to carboxylic acid (—COOH) also includes the anionic (carboxylate) form (—COO⁻), a salt or solvate thereof, as well as conventional protected forms. Similarly, a reference to an amino group includes the protonated form (—N⁺HR¹R²), a salt or solvate of the amino group, for example, a hydrochloride salt, as well as conventional protected forms of an amino group. Similarly, a reference to a hydroxyl group also includes the anionic form (—O⁻), a salt or solvate thereof, as well as conventional protected forms.

Salts

It may be convenient or desirable to prepare, purify, and/or handle a corresponding salt of the active compound (the Conjugate), for example, a pharmaceutically-acceptable salt. Examples of pharmaceutically acceptable salts are discussed in Berge, et al., J. Pharm. Sci., 66, 1-19 (1977).

For example, if the compound is anionic, or has a functional group which may be anionic (e.g. —COOH may be —COO⁻), then a salt may be formed with a suitable cation. Examples of suitable inorganic cations include, but are not limited to, alkali metal ions such as Na⁺ and K⁺, alkaline earth cations such as Ca²⁺ and Mg²⁺, and other cations such as Al⁺³. Examples of suitable organic cations include, but are not limited to, ammonium ion (i.e. NH₄ ⁺) and substituted ammonium ions (e.g. NH₃R⁺, NH₂R₂ ⁺, NHR₃ ⁺, NR₄ ⁺). Examples of some suitable substituted ammonium ions are those derived from: ethylamine, diethylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CH₃)₄ ⁺.

If the Conjugate is cationic, or has a functional group which may be cationic (e.g. —NH₂ may be —NH₃ ⁺), then a salt may be formed with a suitable anion. Examples of suitable inorganic anions include, but are not limited to, those derived from the following inorganic acids: hydrochloric, hydrobromic, hydroiodic, sulfuric, sulfurous, nitric, nitrous, phosphoric, and phosphorous.

Examples of suitable organic anions include, but are not limited to, those derived from the following organic acids: 2-acetyoxybenzoic, acetic, ascorbic, aspartic, benzoic, camphorsulfonic, cinnamic, citric, edetic, ethanedisulfonic, ethanesulfonic, fumaric, glucheptonic, gluconic, glutamic, glycolic, hydroxymaleic, hydroxynaphthalene carboxylic, isethionic, lactic, lactobionic, lauric, maleic, malic, methanesulfonic, mucic, oleic, oxalic, palmitic, pamoic, pantothenic, phenylacetic, phenylsulfonic, propionic, pyruvic, salicylic, stearic, succinic, sulfanilic, tartaric, toluenesulfonic, and valeric. Examples of suitable polymeric organic anions include, but are not limited to, those derived from the following polymeric acids: tannic acid, carboxymethyl cellulose.

Solvates

It may be convenient or desirable to prepare, purify, and/or handle a corresponding solvate of the Conjugate(s). The term “solvate” is used herein in the conventional sense to refer to a complex of solute (e.g. active Conjugate, salt of active Conjugate) and solvent. If the solvent is water, the solvate may be conveniently referred to as a hydrate, for example, a mono-hydrate, a di-hydrate, a tri-hydrate, etc.

Carbinolamines

The invention includes Conjugate where a solvent adds across the imine bond of the PBD moiety, which is illustrated below for a PBD monomer where the solvent is water or an alcohol (R^(A)OH, where R^(A) is C₁₋₄ alkyl):

These forms can be called the carbinolamine and carbinolamine ether forms of the PBD. The balance of these equilibria depend on the conditions in which the compounds are found, as well as the nature of the moiety itself.

These particular compounds may be isolated in solid form, for example, by lyophilisation.

Isomers

Certain compounds may exist in one or more particular geometric, optical, enantiomeric, diasteriomeric, epimeric, atropic, stereoisomeric, tautomeric, conformational, or anomeric forms, including but not limited to, cis- and trans-forms; E- and Z-forms; c-, t-, and r-forms; endo- and exo-forms; R-, S-, and meso-forms; D- and L-forms; d- and l-forms; (+) and (−) forms; keto-, enol-, and enolate-forms; syn- and anti-forms; synclinal- and anticlinal-forms; α- and β-forms; axial and equatorial forms; boat-, chair-, twist-, envelope-, and halfchair-forms; and combinations thereof, hereinafter collectively referred to as “isomers” (or “isomeric forms”).

Note that, except as discussed below for tautomeric forms, specifically excluded from the term “isomers”, as used herein, are structural (or constitutional) isomers (i.e. isomers which differ in the connections between atoms rather than merely by the position of atoms in space). For example, a reference to a methoxy group, —OCH₃, is not to be construed as a reference to its structural isomer, a hydroxymethyl group, —CH₂OH. Similarly, a reference to ortho-chlorophenyl is not to be construed as a reference to its structural isomer, meta-chlorophenyl. However, a reference to a class of structures may well include structurally isomeric forms falling within that class (e.g. C₁₋₇ alkyl includes n-propyl and iso-propyl; butyl includes n-, iso-, sec-, and tert-butyl; methoxyphenyl includes ortho-, meta-, and para-methoxyphenyl).

The above exclusion does not pertain to tautomeric forms, for example, keto-, enol-, and enolate-forms, as in, for example, the following tautomeric pairs: keto/enol (illustrated below), imine/enamine, amide/imino alcohol, amidine/amidine, nitroso/oxime, thioketone/enethiol, N-nitroso/hyroxyazo, and nitro/aci-nitro.

Note that specifically included in the term “isomer” are compounds with one or more isotopic substitutions. For example, H may be in any isotopic form, including ¹H, ²H (D), and ³H (T); C may be in any isotopic form, including ¹²C, ¹³C, and ¹⁴C; O may be in any isotopic form, including ¹⁶O and ¹⁸O; and the like.

Unless otherwise specified, a reference to a particular compound or Conjugate includes all such isomeric forms, including (wholly or partially) racemic and other mixtures thereof. Methods for the preparation (e.g. asymmetric synthesis) and separation (e.g. fractional crystallisation and chromatographic means) of such isomeric forms are either known in the art or are readily obtained by adapting the methods taught herein, or known methods, in a known manner.

General Synthetic Routes

The synthesis of PBD dimer compounds is extensively discussed in the following references, which discussions are incorporated herein by reference:

a) WO 00/12508 (pages 14 to 30);

b) WO 2005/023814 (pages 3 to 10);

c) WO 2004/043963 (pages 28 to 29); and

d) WO 2005/085251 (pages 30 to 39).

Synthesis Route

The Conjugates of the present invention, where R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, can be synthesised from a compound of Compound formula 2:

where R², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of formula II, Prot^(N) is a nitrogen protecting group for synthesis and Prot^(O) is a protected oxygen group for synthesis or an oxo group, by deprotecting the imine bond by standard methods.

The compound produced may be in its carbinolamine or carbinolamine ether form depending on the solvents used. For example if Prot^(N) is Alloc and Prot^(O) is an oxygen protecting group for synthesis, then the deprotection is carried using palladium to remove the N10 protecting group, followed by the elimination of the oxygen protecting group for synthesis. If Prot^(N) is Troc and Prot^(O) is an oxygen protecting group for synthesis, then the deprotection is carried out using a Cd/Pb couple to yield the compound of formula (I). If Prot^(N) is SEM, or an analogous group, and Prot^(O) is an oxo group, then the oxo group can be removed by reduction, which leads to a protected carbinolamine intermediate, which can then be treated to remove the SEM protecting group, followed by the elimination of water. The reduction of the compound of Compound formula 2 can be accomplished by, for example, lithium tetraborohydride, whilst a suitable means for removing the SEM protecting group is treatment with silica gel.

Compounds of Compound formula 2 can be synthesised from a compound of Compound formula 3a:

where R², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of Compound formula 2, by coupling an organometallic derivative comprising R¹², such as an organoboron derivative. The organoboron derivative may be a boronate or boronic acid.

Compounds of Compound formula 2 can be synthesised from a compound of Compound formula 3b:

where R¹², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of Compound formula 2, by coupling an organometallic derivative comprising R², such as an organoboron derivative. The organoboron derivative may be a boronate or boronic acid.

Compounds of Compound formulae 3a and 3b can be synthesised from a compound of formula 4:

where R², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of Compound formula 2, by coupling about a single equivalent (e.g. 0.9 or 1 to 1.1 or 1.2) of an organometallic derivative, such as an organoboron derivative, comprising R² or R¹².

The couplings described above are usually carried out in the presence of a palladium catalyst, for example Pd(PPh₃)₄, Pd(OCOCH₃)₂, PdCl₂, or Pd₂(dba)₃. The coupling may be carried out under standard conditions, or may also be carried out under microwave conditions.

The two coupling steps are usually carried out sequentially. They may be carried out with or without purification between the two steps. If no purification is carried out, then the two steps may be carried out in the same reaction vessel. Purification is usually required after the second coupling step. Purification of the compound from the undesired by-products may be carried out by column chromatography or ion-exchange separation.

The synthesis of compounds of Compound formula 4 where Prot^(O) is an oxo group and Prot^(N) is SEM are described in detail in WO 00/12508, which is incorporated herein by reference. In particular, reference is made to scheme 7 on page 24, where the above compound is designated as intermediate P. This method of synthesis is also described in WO 2004/043963.

The synthesis of compounds of Compound formula 4 where Prot^(O) is a protected oxygen group for synthesis are described in WO 2005/085251, which synthesis is herein incorporated by reference.

Compounds of formula I where R¹⁰ and R^(10′) are H and R¹¹ and R^(11′) are SO_(z)M, can be synthesised from compounds of formula I where R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, by the addition of the appropriate bisulphite salt or sulphinate salt, followed by an appropriate purification step. Further methods are described in GB 2 053 894, which is herein incorporated by reference.

Nitrogen Protecting Groups for Synthesis

Nitrogen protecting groups for synthesis are well known in the art. In the present invention, the protecting groups of particular interest are carbamate nitrogen protecting groups and hemi-aminal nitrogen protecting groups.

Carbamate nitrogen protecting groups have the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 503 to 549 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

Particularly preferred protecting groups include Troc, Teoc, Fmoc, BOC, Doc, Hoc, TcBOC, 1-Adoc and 2-Adoc.

Other possible groups are nitrobenzyloxycarbonyl (e.g. 4-nitrobenzyloxycarbonyl) and 2-(phenylsulphonyl)ethoxycarbonyl.

Those protecting groups which can be removed with palladium catalysis are not preferred, e.g. Alloc.

Hemi-aminal nitrogen protecting groups have the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 633 to 647 as amide protecting groups of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference. The groups disclosed herein can be applied to compounds for use in the present invention. Such groups include, but are not limited to, SEM, MOM, MTM, MEM, BOM, nitro or methoxy substituted BOM, and Cl₃CCH₂OCH₂—.

Protected Oxygen Group for Synthesis

Protected oxygen group for synthesis are well known in the art. A large number of suitable oxygen protecting groups are described on pages 23 to 200 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

Classes of particular interest include silyl ethers, methyl ethers, alkyl ethers, benzyl ethers, esters, acetates, benzoates, carbonates, and sulfonates.

Preferred oxygen protecting groups include acetates, TBS and THP.

Further Preferences

The following preferences may apply to all aspects of the invention as described above, or may relate to a single aspect. The preferences may be combined together in any combination.

In some embodiments, R^(6′), R^(7′), R^(9′), R^(10′), R^(11′) and Y′ are preferably the same as R⁶, R⁷, R⁹, R¹⁰, R¹¹ and Y respectively.

Dimer Link

Y and Y′ are preferably O.

R″ is preferably a C₃₋₇ alkylene group with no substituents. More preferably R″ is a C₃, C₅ or C₇ alkylene.

R⁶ to R⁹

R⁹ is preferably H.

R⁶ is preferably selected from H, OH, OR, SH, NH₂, nitro and halo, and is more preferably H or halo, and most preferably is H.

R⁷ is preferably selected from H, OH, OR, SH, SR, NH₂, NHR, NRR′, and halo, and more preferably independently selected from H, OH and OR, where R is preferably selected from optionally substituted C₁₋₇ alkyl, C₃₋₁₀ heterocyclyl and C₅₋₁₀ aryl groups. R may be more preferably a C₁₋₄ alkyl group, which may or may not be substituted. A substituent of interest is a C₅₋₆ aryl group (e.g. phenyl). Particularly preferred substituents at the 7-positions are OMe and OCH₂Ph.

These preferences apply to R^(9′), R^(6′) and R^(7′) respectively.

R²

A in R² may be phenyl group or a C₅₋₇ heteroaryl group, for example furanyl, thiophenyl and pyridyl. In some embodiments, A is preferably phenyl. In other embodiments, A is preferably thiophenyl, for example, thiophen-2-yl and thiophen-3-yl.

X is a group selected from the list comprising: —O—, —S—, —C(O)O—, —C(O)—, —NH(C═O)— and —N(R^(N))—, wherein R^(N) is selected from the group comprising H and C₁₋₄ alkyl. X may preferably be: —O—, —S—, —C(O)O—, —NH(C═O)— or —NH—, and may more preferably be: —O—, —S—, or —NH—, and most preferably is —NH—.

Q²-X may be on any of the available ring atoms of the C₅₋₇ aryl group, but is preferably on a ring atom that is not adjacent the bond to the remainder of the compound, i.e. it is preferably β or γ to the bond to the remainder of the compound. Therefore, where the C₅₋₇ aryl group (A) is phenyl, the substituent (Q¹-X) is preferably in the meta- or para-positions, and more preferably is in the para-position.1

In some embodiments, Q¹ is a single bond. In these embodiments, Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and is from 1 to 3. In some of these embodiments, Q² is a single bond. In other embodiments, Q² is —Z—(CH₂)_(n)—. In these embodiments, Z may be O or S and n may be 1 or n may be 2. In other of these embodiments, Z may be a single bond and n may be 1.

In other embodiments, Q¹ is —CH═CH—.

In some embodiments, R2 may be -A-CH₂—X and -A-X. In these embodiments, X may be —O—, —S—, —C(O)O—, —C(O)— and —NH—. In particularly preferred embodiments, X may be —NH—.

R¹²

R¹² may be a C₅₋₇ aryl group. A C₅₋₇ aryl group may be a phenyl group or a C₅₋₇ heteroaryl group, for example furanyl, thiophenyl and pyridyl. In some embodiments, R¹² is preferably phenyl. In other embodiments, R¹² is preferably thiophenyl, for example, thiophen-2-yl and thiophen-3-yl.

R¹² may be a C₈₋₁₀ aryl, for example a quinolinyl or isoquinolinyl group. The quinolinyl or isoquinolinyl group may be bound to the PBD core through any available ring position. For example, the quinolinyl may be quinolin-2-yl, quinolin-3-yl, quinolin-4yl, quinolin-5-yl, quinolin-6-yl, quinolin-7-yl and quinolin-8-yl. Of these quinolin-3-yl and quinolin-6-yl may be preferred. The isoquinolinyl may be isoquinolin-1-yl, isoquinolin-3-yl, isoquinolin-4yl, isoquinolin-5-yl, isoquinolin-6-yl, isoquinolin-7-yl and isoquinolin-8-yl. Of these isoquinolin-3-yl and isoquinolin-6-yl may be preferred.

R¹² may bear any number of substituent groups. It preferably bears from 1 to 3 substituent groups, with 1 and 2 being more preferred, and singly substituted groups being most preferred. The substituents may be any position.

Where R¹² is C₅₋₇ aryl group, a single substituent is preferably on a ring atom that is not adjacent the bond to the remainder of the compound, i.e. it is preferably β or γ to the bond to the remainder of the compound. Therefore, where the C₅₋₇ aryl group is phenyl, the substituent is preferably in the meta- or para-positions, and more preferably is in the para-position.

Where R¹² is a C₈₋₁₀ aryl group, for example quinolinyl or isoquinolinyl, it may bear any number of substituents at any position of the quinoline or isoquinoline rings. In some embodiments, it bears one, two or three substituents, and these may be on either the proximal and distal rings or both (if more than one substituent).

R¹² Substituents

If a substituent on R¹² is halo, it is preferably F or Cl, more preferably Cl.

If a substituent on R¹² is ether, it may in some embodiments be an alkoxy group, for example, a C₁₋₇ alkoxy group (e.g. methoxy, ethoxy) or it may in some embodiments be a C₅₋₇ aryloxy group (e.g. phenoxy, pyridyloxy, furanyloxy). The alkoxy group may itself be further substituted, for example by an amino group (e.g. dimethylamino).

If a substituent on R¹² is C₁₋₇ alkyl, it may preferably be a C₁₋₄ alkyl group (e.g. methyl, ethyl, propyl, butyl).

If a substituent on R¹² is C₃₋₇ heterocyclyl, it may in some embodiments be C₆ nitrogen containing heterocyclyl group, e.g. morpholino, thiomorpholino, piperidinyl, piperazinyl. These groups may be bound to the rest of the PBD moiety via the nitrogen atom. These groups may be further substituted, for example, by C₁₋₄ alkyl groups. If the C₆ nitrogen containing heterocyclyl group is piperazinyl, the said further substituent may be on the second nitrogen ring atom.

If a substituent on R¹² is bis-oxy-C₁₋₃ alkylene, this is preferably bis-oxy-methylene or bis-oxy-ethylene.

Particularly preferred substituents for R¹² include methoxy, ethoxy, fluoro, chloro, cyano, bis-oxy-methylene, methyl-piperazinyl, morpholino and methyl-thiophenyl. Another particularly preferred substituent for R¹² is dimethylaminopropyloxy.

R¹² Groups

Particularly preferred substituted R¹² groups include, but are not limited to, 4-methoxy-phenyl, 3-methoxyphenyl, 4-ethoxy-phenyl, 3-ethoxy-phenyl, 4-fluoro-phenyl, 4-chloro-phenyl, 3,4-bisoxymethylene-phenyl, 4-methylthiophenyl, 4-cyanophenyl, 4-phenoxyphenyl, quinolin-3-yl and quinolin-6-yl, isoquinolin-3-yl and isoquinolin-6-yl, 2-thienyl, 2-furanyl, methoxynaphthyl, and naphthyl. Another possible substituted R¹² group is 4-nitrophenyl.

M and Z

It is preferred that M and M′ are monovalent pharmaceutically acceptable cations, and are more preferably Na⁺.

z is preferably 3.

EXAMPLES

General Experimental Methods

Optical rotations were measured on an ADP 220 polarimeter (Bellingham Stanley Ltd.) and concentrations (c) are given in g/100 mL. Melting points were measured using a digital melting point apparatus (Electrothermal). IR spectra were recorded on a Perkin-Elmer Spectrum 1000 FT IR Spectrometer. ¹H and ¹³C NMR spectra were acquired at 300 K using a Bruker Avance NMR spectrometer at 400 and 100 MHz, respectively. Chemical shifts are reported relative to TMS (δ=0.0 ppm), and signals are designated as s (singlet), d (doublet), t (triplet), dt (double triplet), dd (doublet of doublets), ddd (double doublet of doublets) or m (multiplet), with coupling constants given in Hertz (Hz). Mass spectroscopy (MS) data were collected using a Waters Micromass ZQ instrument coupled to a Waters 2695 HPLC with a Waters 2996 PDA. Waters Micromass ZQ parameters used were: Capillary (kV), 3.38; Cone (V), 35; Extractor (V), 3.0; Source temperature (° C.), 100; Desolvation Temperature (° C.), 200; Cone flow rate (L/h), 50; De-solvation flow rate (L/h), 250. High-resolution mass spectroscopy (HRMS) data were recorded on a Waters Micromass QTOF Global in positive W-mode using metal-coated borosilicate glass tips to introduce the samples into the instrument. Thin Layer Chromatography (TLC) was performed on silica gel aluminium plates (Merck 60, F₂₅₄), and flash chromatography utilised silica gel (Merck 60, 230-400 mesh ASTM). Except for the HOBt (NovaBiochem) and solid-supported reagents (Argonaut), all other chemicals and solvents were purchased from Sigma-Aldrich and were used as supplied without further purification. Anhydrous solvents were prepared by distillation under a dry nitrogen atmosphere in the presence of an appropriate drying agent, and were stored over 4 Å molecular sieves or sodium wire. Petroleum ether refers to the fraction boiling at 40-60° C.

Compound 1b was synthesised as described in WO 00/012508 (compound 210), which is herein incorporated by reference.

General LC/MS conditions: The HPLC (Waters Affiance 2695) was run using a mobile phase of water (A) (formic acid 0.1%) and acetonitrile (B) (formic acid 0.1%). Gradient: initial composition 5% B over 1.0 min then 5% B to 95% B within 3 min. The composition was held for 0.5 min at 95% B, and then returned to 5% B in 0.3 minutes. Total gradient run time equals 5 min. Flow rate 3.0 mL/min, 400 μL was split via a zero dead volume tee piece which passes into the mass spectrometer. Wavelength detection range: 220 to 400 nm. Function type: diode array (535 scans). Column: Phenomenex® Onyx Monolithic C18 50×4.60 mm

LC/MS conditions specific for compounds protected by both a Troc and a TBDMs group: Chromatographic separation of Troc and TBDMS protected compounds was performed on a Waters Alliance 2695 HPLC system utilizing a Onyx Monolitic reversed-phase column (3 μm particles, 50×4.6 mm) from Phenomenex Corp. Mobile-phase A consisted of 5% acetonitrile—95% water containing 0.1% formic acid, and mobile phase B consisted of 95% acetonitrile—5% water containing 0.1% formic acid. After 1 min at 5% B, the proportion of B was raised to 95% B over the next 2.5 min and maintained at 95% B for a further 1 min, before returning to 95% A in 10 s and re-equilibration for a further 50 sec, giving a total run time of 5.0 min. The flow rate was maintained at 3.0 mL/min.

LC/MS conditions specific for compound 33: LC was run on a Waters 2767 sample Manager coupled with a Waters 2996 photodiode array detector and a Waters ZQ single quadruple mass Spectrometer. The column used was Luna Phenyl-Hexyl 150×4.60 mm, 5 μm, Part no. 00F-4257-E0 (Phenomenex). The mobile phases employed were: Mobile phase A: 100% of HPLC grade water (0.05% triethylarnine), pH=7 Mobile phase B: 20% of HPLC grade water and 80% of HPLC grade acetonitrile (0.05% triethylamine), pH=7

The gradients used were:

Time Flow Rate (min) (ml/min) % A % B Initial 1.50 90 10 1.0 1.50 90 10 16.0 1.50 64 36 30.0 1.50 5 95 31.0 1.50 90 10 32.0 1.50 90 10

Mass Spectrometry was carried out in positive ion mode and SIR (selective ion monitor) and the ion monitored was m/z=727.2.

Synthesis of Key Intermediates

(a) 1,1′-[[(Propane-1,3-diyl)dioxy]bis[(5-methoxy-2-nitro-1,4-phenylene)carbonyl]]bis[(2S,4R)-methyl-4-hydroxypyrrolidine-2-carboxylate] (2a)

Method A: A catalytic amount of DMF (2 drops) was added to a stirred solution of the nitro-acid 1a (1.0 g, 2.15 mmol) and oxalyl chloride (0.95 mL, 1.36 g, 10.7 mmol) in dry THF (20 mL). The reaction mixture was allowed to stir for 16 hours at room temperature and the solvent was removed by evaporation in vacuo. The resulting residue was re-dissolved in dry THE (20 mL) and the acid chloride solution was added dropwise to a stirred mixture of (2,S,4R)-methyl-4-hydroxypyrrolidine-2-carboxylate hydrochloride (859 mg, 4.73 mmol) and TEA (6.6 mL, 4.79 g, 47.3 mmol) in THF (10 mL) at −30° C. (dry ice/ethylene glycol) under a nitrogen atmosphere. The reaction mixture was allowed to warm to room temperature and stirred for a further 3 hours after which time TLC (95:5 v/v CHCl₃/MeOH) and LC/MS (2.45 min (ES+) m/z (relative intensity) 721 ([M+H]⁺, 20)) revealed formation of product. Excess THF was removed by rotary evaporation and the resulting residue was dissolved in DCM (50 mL). The organic layer was washed with 1N HCl (2×15 mL), saturated NaHCO₃ (2×15 mL), H₂O (20 mL), brine (30 mL) and dried (MgSO₄). Filtration and evaporation of the solvent gave the crude product as a dark coloured oil. Purification by flash chromatography (gradient elution: 100% CHCl₃ to 96:4 v/v CHCl₃/MeOH) isolated the pure amide 2a as an orange coloured glass (840 mg, 54%).

Method B: Oxalyl chloride (9.75 mL, 14.2 g, 111 mmol) was added to a stirred suspension of the nitro-acid 1a (17.3 g, 37.1 mmol) and DMF (2 mL) in anhydrous DCM (200 mL). Following initial effervescence the reaction suspension became a solution and the mixture was allowed to stir at room temperature for 16 hours. Conversion to the acid chloride was confirmed by treating a sample of the reaction mixture with MeOH and the resulting bis-methyl ester was observed by LC/MS. The majority of solvent was removed by evaporation in vacuo, the resulting concentrated solution was re-dissolved in a minimum amount of dry DCM and triturated with diethyl ether. The resulting yellow precipitate was collected by filtration, washed with cold diethyl ether and dried for 1 hour in a vacuum oven at 40° C. The solid acid chloride was added portionwise over a period of 25 minutes to a stirred suspension of (2S,4R)-methyl-4-hydroxypyrrolidine-2-carboxylate hydrochloride (15.2 g, 84.0 mmol) and TEA (25.7 mL, 18.7 g, 185 mmol) in DCM (150 mL) at −40° C. (dry ice/CH₃CN). Immediately, the reaction was complete as judged by LC/MS (2.47 min (ES+) m/z (relative intensity) 721 ([M+H]^(+.), 100)). The mixture was diluted with DCM (150 mL) and washed with 1N HCl (300 mL), saturated NaHCO₃ (300 mL), brine (300 mL), filtered (through a phase separator) and the solvent evaporated in vacuo to give the pure product 2a as an orange solid (21.8 g, 82%).

Analytical Data: [α]²² _(D)=−46.1° (c=0.47, CHCl₃); ¹H NMR (400 MHz, CDCl₃) (rotamers) δ 7.63 (s, 2H), 6.82 (s, 2H), 4.79-4.72 (m, 2H), 4.49-4.28 (m, 6H), 3.96 (s, 6H), 3.79 (s, 6H), 3.46-3.38 (m, 2H), 3.02 (d, 2H, J=11.1 Hz), 2.48-2.30 (m, 4H), 2.29-2.04 (m, 4H); ¹³C NMR (100 MHz, CDCl₃) (rotamers) δ 172.4, 166.7, 154.6, 148.4, 137.2, 127.0, 109.7, 108.2, 69.7, 65.1, 57.4, 57.0, 56.7, 52.4, 37.8, 29.0; IR (ATR, CHCl₃) 3410 (br), 3010, 2953, 1741, 1622, 1577, 1519, 1455, 1429, 1334, 1274, 1211, 1177, 1072, 1050, 1008, 871 cm⁻¹; MS (ES⁺) m/z (relative intensity) 721 ([M+H]^(+.), 47), 388 (80); HRMS [M+H]^(+.) theoretical C₃₁H₃₆N₄O₁₆ m/z 721.2199, found (ES⁺) m/z 721.2227.

(a) 1,1′-[[(Pentane-1,5-diyl)dioxy]bis[(5-methoxy-2-nitro-1,4-phenylene)carbonyl]]bis[(2S,4R)-methyl-4-hydroxypyrrolidine-2-carboxylate] (2b)

Preparation from 1b according to Method B gave the pure product as an orange foam (75.5 g, 82%).

Analytical Data: (ES⁺) m/z (relative intensity) 749 ([M+H]^(+.), 100).

(b) 1,1′-[[(Propane-1,3-diyl)dioxy]bis(11aS2R)-2-(hydroxy)-7-methoxy-1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (3a)

Method A: A suspension of 10% Pd/C (7.5 g, 10% w/w) in DMF (40 mL) was added to a solution of the nitro-ester 2a (75 g, 104 mmol) in DMF (360 mL). The suspension was hydrogenated in a Parr hydrogenation apparatus over 8 hours. Progress of the reaction was monitored by LC/MS (2.12 min (ES+) m/z (relative intensity) 597 ([M+H]^(+.), 100), (ES−) m/z (relative intensity) 595 ([M+H]^(+.), 100) after the hydrogen uptake had stopped. Solid Pd/C was removed by filtration and the filtrate was concentrated by rotary evaporation under vacuum (below 10 mbar) at 40° C. to afford a dark oil containing traces of DMF and residual charcoal. The residue was digested in EtOH (500 mL) at 40° C. on a water bath (rotary evaporator bath) and the resulting suspension was filtered through celite and washed with ethanol (500 mL) to give a clear filtrate. Hydrazine hydrate (10 mL, 321 mmol) was added to the solution and the reaction mixture was heated at reflux. After 20 minutes the formation of a white precipitate was observed and reflux was allowed to continue for a further 30 minutes. The mixture was allowed to cool down to room temperature and the precipitate was retrieved by filtration, washed with diethyl ether (2*1 volume of precipitate) and dried in a vacuum desiccator to provide 3a (50 g, 81%).

Method B: A solution of the nitro-ester 2a (6.80 g, 9.44 mmol) in MeOH (300 mL) was added to Raney™ nickel (4 large spatula ends of a ˜50% slurry in H₂O) and anti-bumping granules in a 3-neck round bottomed flask. The mixture was heated at reflux and then treated dropwise with a solution of hydrazine hydrate (5.88 mL, 6.05 g, 188 mmol) in MeOH (50 mL) at which point vigorous effervescence was observed. When the addition was complete (˜30 minutes) additional Raney™ nickel was added carefully until effervescence had ceased and the initial yellow colour of the reaction mixture was discharged. The mixture was heated at reflux for a further 30 minutes at which point the reaction was deemed complete by TLC (90:10 v/v CHCl₃/MeOH) and LC/MS (2.12 min (ES+) m/z (relative intensity) 597 ([M+H]^(+.), 100)). The reaction mixture was allowed to cool to around 40° C. and then excess nickel removed by filtration through a sinter funnel without vacuum suction. The filtrate was reduced in volume by evaporation in vacuo at which point a colourless precipitate formed which was collected by filtration and dried in a vacuum desiccator to provide 3a (5.40 g, 96%).

Analytical Data: [α]²⁷ _(D)=+404° (c=0.10, DMF); ¹H NMR (400 MHz, DMSO-d₆) δ 10.2 (s, 2H, NH), 7.26 (s, 2H), 6.73 (s, 2H), 5.11 (d, 2H, J=3.98 Hz, OH), 4.32-4.27 (m, 2H), 4.19-4.07 (m, 6H), 3.78 (s, 6H), 3.62 (dd, 2H, J=12.1, 3.60 Hz), 3.43 (dd, 2H, J=12.0, 4.72 Hz), 2.67-2.57 (m, 2H), 2.26 (p, 2H, J=5.90 Hz), 1.99-1.89 (m, 2H); ¹³C NMR (100 MHz, DMSO-d₆) δ 169.1, 164.0, 149.9, 144.5, 129.8, 117.1, 111.3, 104.5, 54.8, 54.4, 53.1, 33.5, 27.5; IR (ATR, neat) 3438, 1680, 1654, 1610, 1605, 1516, 1490, 1434, 1379, 1263, 1234, 1216, 1177, 1156, 1115, 1089, 1038, 1018, 952, 870 cm⁻¹; MS (ES⁺) m/z (relative intensity) 619 ([M+Na]^(+.), 10), 597 ([M+H]^(+.), 52), 445 (12), 326 (11); HRMS [M+H]^(+.) theoretical C₂₉H₃₂N₄O₁₀ m/z 597.2191, found (ES⁺) m/z 597.2205.

(b) 1,1′-[[(Pentane-1,5-diyl)dioxy]bis(11aS,2R)-2-(hydroxy)-7-methoxy-1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (3b)

Preparation from 2b according to Method A gave the product as a white solid (22.1 g, 86%).

Analytical Data: MS (ES⁻) m/z (relative intensity) 623.3 ([M−H]^(+.), 100);

(c) 1,1′-[[(Propane-1,3-diyl)dioxy]bis(11aS,2R)-2-(tert-butyldimethylsilyloxy)-7-methoxy-1,2,3,10,11,11a-hexahydro-5H-1-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (4a)

TBSCl (317 mg, 2.1 mmol) and imidazole (342 mg, 5.03 mmol) were added to a cloudy solution of the tetralactam 3a (250 mg, 0.42 mmol) in anhydrous DMF (6 mL). The mixture was allowed to stir under a nitrogen atmosphere for 3 hours after which time the reaction was deemed complete as judged by LC/MS (3.90 min (ES+) m/z (relative intensity) 825 ([M+H]^(+.), 100)). The reaction mixture was poured onto ice (˜25 mL) and allowed to warm to room temperature with stirring. The resulting white precipitate was collected by vacuum filtration, washed with H₂O, diethyl ether and dried in the vacuum desiccator to provide pure 4a (252 mg, 73%).

Analytical Data: [α]²³ _(D)=+234° (c=0.41, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ 8.65 (s, 2H, NH), 7.44 (s, 2H), 6.54 (s, 2H), 4.50 (p, 2H, J=5.38 Hz), 4.21-4.10 (m, 6H), 3.87 (s, 6H), 3.73-3.63 (m, 4H), 2.85-2.79 (m, 2H), 2.36-2.29 (m, 2H), 2.07-1.99 (m, 2H), 0.86 (s, 18H), 0.08 (s, 12H); ¹³C NMR (100 MHz, CDCl₃) δ 170.4, 165.7, 151.4, 146.6, 129.7, 118.9, 112.8, 105.3, 69.2, 65.4, 56.3, 55.7, 54.2, 35.2, 28.7, 25.7, 18.0, −4.82 and −4.86; IR (ATR, CHCl₃) 3235, 2955, 2926, 2855, 1698, 1695, 1603, 1518, 1491, 1446, 1380, 1356, 1251, 1220, 1120, 1099, 1033 cm⁻¹; MS (ES⁺) m/z (relative intensity) 825 ([M+H]^(+.), 62), 721 (14), 440 (38): HRMS [M+H]^(+.) theoretical C₄₁H₆₀N₄O₁₀Si₂ m/z 825.3921, found (ES⁺) m/z 825.3948.

(c) 1,1′-[[(Pentane-1,5-diyl)dioxy]bis(11aS,2R)-2-(tert-butyldimethylsilyloxy)-7-methoxy-1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (4b)

Preparation from 3b according to the above method gave the product as a white solid (27.3 g, 93%).

Analytical Data: MS (ES⁺) m/z (relative intensity) 853.8 ([M+H]^(+.), 100), (ES⁻) m/z (relative intensity) 851.6 ([M−H]^(−.), 100.

(d) 1,1′-[[(Propane-1,3-diyl)dioxy]bis(11aS,2R)-2-(tert-butyldimethylsilyloxy)-7-methoxy-10-((2-(trimethylsifyl)ethoxy)methyl)-1,2,3,10,11,11a-hexahydro-5H-1-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (5a)

A solution of n-BuLi (4.17 mL of a 1.6 M solution in hexane, 6.67 mmol) in anhydrous THF (10 mL) was added dropwise to a stirred suspension of the tetralactam 4a (2.20 g, 2.67 mmol) in anhydrous THF (30 mL) at −30° C. (dry ice/ethylene glycol) under a nitrogen atmosphere. The reaction mixture was allowed to stir at this temperature for 1 hour (now a reddish orange colour) at which point a solution of SEMCl (1.18 mL, 1.11 g, 6.67 mmol) in anhydrous THF (10 mL) was added dropwise. The reaction mixture was allowed to slowly warm to room temperature and was stirred for 16 hours under a nitrogen atmosphere. The reaction was deemed complete as judged by TLC (EtOAc) and LC/MS (4.77 min (ES+) m/z (relative intensity) 1085 ([M+H]^(+.), 100)). The THF was removed by evaporation in vacuo and the resulting residue dissolved in EtOAc (60 mL), washed with H₂O (20 mL), brine (20 mL), dried (MgSO₄) filtered and evaporated in vacuo to provide the crude product. Purification by flash chromatography (80:20 v/v Hexane/EtOAc) gave the pure N10-SEM-protected tetralactam 5a as an oil (2.37 g, 82%).

Analytical Data: [α]²³ _(D)=+163° (c=0.41, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ 7.33 (s, 2H), 7.22 (s, 2H), 5.47 (d, 2H, J=9.98 Hz), 4.68 (d, 2H, J=9.99 Hz), 4.57 (p, 2H, J=5.77 Hz), 4.29-4.19 (m, 6H), 3.89 (s, 6H), 3.79-3.51 (m, 8H), 2.87-2.81 (m, 2H), 2.41 (p, 2H, J=5.81 Hz), 2.03-1.90 (m, 2H), 1.02-0.81 (m, 22H), 0.09 (s, 12H), 0.01 (s, 18H); ¹³C NMR (100 MHz, CDCl₃) δ 170.0, 165.7, 151.2, 147.5, 133.8, 121.8, 111.6, 106.9, 78.1, 69.6, 67.1, 65.5, 56.6, 56.3, 53.7, 35.6, 30.0, 25.8, 18.4, 18.1, −1.24, −4.73; IR (ATR, CHCl₃) 2951, 1685, 1640, 1606, 1517, 1462, 1433, 1360, 1247, 1127, 1065 cm⁻¹; MS (ES⁺) m/z (relative intensity) 1113 ([M+Na]^(+.), 48), 1085 ([M+H]^(+.), 100), 1009 (5), 813 (6); HRMS [M+H]^(+.) theoretical C₅₃H₈₈N₄O₁₂Si₄ m/z 1085.5548, found (ES⁺) m/z 1085.5542.

(d) 1,1′-[[(Pentane1,5-diyl)dioxy]bis(11aS,2R)-2-(tert-butyldimethylsilyloxy)-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (5b)

Preparation from 4b according to the above method gave the product as a pale orange foam (46.9 g, 100%), used without further purification.

Analytical Data: MS (ES⁺) m/z (relative intensity) 1114 ([M+H]^(+.), 90), (ES⁻) m/z (relative intensity) 1158 ([M+2Na]^(−.), 100).

(e) 1,1′-[[(Propane-1,3-diyl)dioxy]bis(11aS,2R)-2-hydroxy-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (6a)

A solution of TBAF (5.24 mL of a 1.0 M solution in THF, 5.24 mmol) was added to a stirred solution of the bis-silyl ether 5a (2.58 g, 2.38 mmol) in THF (40 mL) at room temperature. After stirring for 3.5 hours, analysis of the reaction mixture by TLC (95:5 v/v CHCl₃/MeOH) revealed completion of reaction. The reaction mixture was poured into a solution of saturated NH₄Cl (100 mL) and extracted with EtOAc (3×30 mL). The combined organic layers were washed with brine (60 mL), dried (MgSO₄), filtered and evaporated in vacuo to provide the crude product. Purification by flash chromatography (gradient elution: 100% CHCl₃ to 96:4 v/v CHCl₃/MeOH) gave the pure tetralactam 6a as a white foam (1.78 g, 87%).

Analytical Data: [α]³⁰ _(D)=+202° (c=0.34, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ 7.28 (s, 2H), 7.20 (s, 2H), 5.44 (d, 2H, J=10.0 Hz), 4.72 (d, 2H, J=10.0 Hz), 4.61-4.58 (m, 2H), 4.25 (t, 4H, J=5.83 Hz), 4.20-4.16 (m, 2H), 3.91-3.85 (m, 8H), 3.77-3.54 (m, 6H), 3.01 (br s, 2H, OH), 2.96-2.90 (m, 2H), 2.38 (p, 2H, J=5.77 Hz), 2.11-2.05 (m, 2H), 1.00-0.91 (m, 4H), 0.00 (s, 18H); ¹³C NMR (100 MHz, CDCl₃) δ 169.5, 165.9, 151.3, 147.4, 133.7, 121.5, 111.6, 106.9, 79.4, 69.3, 67.2, 65.2, 56.5, 56.2, 54.1, 35.2, 29.1, 18.4, −1.23; IR (ATR, CHCl₃) 2956, 1684, 1625, 1604, 1518, 1464, 1434, 1361, 1238, 1058, 1021 cm⁻¹; MS (ES⁺) m/z (relative intensity) 885 ([M+29]^(+.), 70), 857 ([M+H]^(+.), 100), 711 (8), 448 (17); HRMS [M+H]^(+.) theoretical C₄₁H₆₀N₄O₁₂Si₂ m/z 857.3819, found (ES⁺) m/z 857.3826.

(e) 1,1′-[[(Pentane-1,5-diyl)dioxy]bis(11aS,2R)-2-hydroxy-7-methoxy-10-((2-(trimethylsilyl)ethoxy)methyl)-1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (6b)

Preparation from 5b according to the above method gave the product as a white foam (15.02 g).

Analytical Data: MS (ES⁺) m/z (relative intensity) 886 ([M+H]^(+.), 10), 739.6 (100), (ES⁻) m/z (relative intensity) 884 ([M−H]^(−.), 40).

(f) 1,1′-[[(Propene-1,3-diyl)dioxy]bis[(11aS)-11-sulpho-7-methoxy-2-oxo-10-((2-(trimethylsilyl)ethoxy)methyl)1,2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5,11-dione]] (7a)

Method A: A 0.37 M sodium hypochlorite solution (142.5 mL, 52.71 mmol, 2.4 eq) was added dropwise to a vigorously stirred mixture of the diol 6a (18.8 g, 21.96 mmol, 1 eq), TEMPO (0.069 g, 0.44 mmol, 0.02 eq) and 0.5 M potassium bromide solution (8.9 mL, 4.4 mmol, 0.2 eq) in DCM (115 mL) at 0° C. The temperature was maintained between 0° C. and 5° C. by adjusting the rate of addition. The resultant yellow emulsion was stirred at 0° C. to 5° C. for 1 hour. TLC (EtOAc) and LC/MS [3.53 min, (ES+) m/z (relative intensity) 875 ([M+Na]^(+.), 50), (ES−) m/z (relative intensity) 852 ([M−H]^(+.), 100)] indicated that reaction was complete.

The reaction mixture was filtered, the organic layer separated and the aqueous layer was backwashed with DCM (×2). The combined organic portions were washed with brine (×1), dried (MgSO₄) and evaporated to give a yellow foam. Purification by flash column chromatography (gradient elution 35/65 v/v n-hexane/EtOAC, 30/70 to 25/75 v/v n-hexane/EtOAC) afforded the bis-ketone 7a as a white foam (14.1 g, 75%).

Sodium hypochlorite solution, reagent grade, available at chlorine 10-13%, was used. This was assumed to be 10% (10 g NaClO in 100 g) and calculated to be 1.34 M in NaClO. A stock solution was prepared from this by diluting it to 0.37 M with water. This gave a solution of approximately pH 14. The pH was adjusted to 9.3 to 9.4 by the addition of solid NaHCO₃. An aliquot of this stock was then used so as to give 2.4 mol eq. for the reaction.

On addition of the bleach solution an initial increase in temperature was observed. The rate of addition was controlled, to maintain the temperature between 0° C. to 5° C. The reaction mixture formed a thick, lemon yellow coloured, emulsion.

The oxidation was an adaptation of the procedure described in Thomas Fey et al., J. Org. Chem., 2001, 66, 8154-8159.

Method B: Solid TCCA (10.6 g, 45.6 mmol) was added portionwise to a stirred solution of the alcohol 6a (18.05 g, 21.1 mmol) and TEMPO (123 mg, 0.78 mmol) in anhydrous DCM (700 mL) at 0° C. (ice/acetone). The reaction mixture was stirred at 0° C. under a nitrogen atmosphere for 15 minutes after which time TLC (EtOAc) and LC/MS [3.57 min (ES+) m/z (relative intensity) 875 ([M+Na]^(+.), 50)] revealed completion of reaction. The reaction mixture was filtered through celite and the filtrate was washed with saturated aqueous NaHCO₃ (400 mL), brine (400 mL), dried (MgSO₄), filtered and evaporated in vacuo to provide the crude product. Purification by flash column chromatography (80:20 v/v EtOAc/Hexane) afforded the bis-ketone 7a as a foam (11.7 g, 65%).

Method C: A solution of anhydrous DMSO (0.72 mL, 0.84 g, 10.5 mmol) in dry DCM (18 mL) was added dropwise over a period of 25 min to a stirred solution of oxalyl chloride (2.63 mL of a 2.0 M solution in DCM, 5.26 mmol) under a nitrogen atmosphere at −60° C. (liq N₂/CHCl₃). After stirring at −55° C. for 20 minutes, a slurry of the substrate 6a (1.5 g, 1.75 mmol) in dry DCM (36 mL) was added dropwise over a period of 30 min to the reaction mixture. After stirring for a further 50 minutes at −55° C., a solution of TEA (3.42 mL, 2.49 g; 24.6 mmol) in dry DCM (18 mL) was added dropwise over a period of 20 min to the reaction mixture. The stirred reaction mixture was allowed to warm to room temperature (˜1.5 h) and then diluted with DCM (50 mL). The organic solution was washed with 1 N HCl (2×25 mL), H₂O (30 mL), brine (30 mL) and dried (MgSO₄). Filtration and evaporation of the solvent in vacuo afforded the crude product which was purified by flash column chromatography (80:20 V/V EtOAc/Hexane) to afford bis-ketone 7a as a foam (835 mg, 56%)

Analytical Data: [α]²⁰ _(D)=+291° (c=0.26, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ 7.32 (s, 2H), 7.25 (s, 2H), 5.50 (d, 2H, J=10.1 Hz), 4.75 (d, 2H, J=10.1 Hz), 4.60 (dd, 2H, J=9.85, 3.07 Hz), 4.31-4.18 (m, 6H), 3.89-3.84 (m, 8H), 3.78-3.62 (m, 4H), 3.55 (dd, 2H, J=19.2, 2.85 Hz), 2.76 (dd, 2H, J=19.2, 9.90 Hz), 2.42 (p, 2H, J=5.77 Hz), 0.98-0.91 (m, 4H), 0.00 (s, 18H); ¹³C NMR (100 MHz, CDCl₃) δ 206.8, 168.8, 165.9, 151.8, 148.0, 133.9, 120.9, 111.6, 107.2, 78.2, 67.3, 65.6, 56.3, 54.9, 52.4, 37.4, 29.0, 18.4, −1.24; IR (ATR, CHCl₃) 2957, 1763, 1685, 1644, 1606, 1516, 1457, 1434, 1360, 1247, 1209, 1098, 1066, 1023 cm⁻¹; MS (ES⁺) m/z (relative intensity) 881 ([M+29]^(+.), 38), 853 ([M+H]^(+.), 100), 707 (8), 542 (12); HRMS [M+H]^(+.) theoretical C₄₁H₅₆N₄O₁₂Si₂ m/z 853.3506, found (ES⁺) m/z 853.3502.

(f) 1,1′-[[(Pentane-1,5-diyl)dioxy]bis[(11aS)-11-sulpho-7-methoxy-2-oxo-10-((2-(trimethylsilyl)ethoxy)methyl)1, 2,3,10,11,11a-hexahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5,11-dione]](7b)

Preparation from 61) according to Method C gave the product as a white foam (10.5 g, 76%).

Analytical Data: MS (ES⁺) m/z (relative intensity) 882 ([M H]^(+.), 30), 735 (100), (ES⁻) m/z (relative intensity) 925 ([M+45]^(−.), 100), 880 ([M−H]^(−.), 70).

(g) 1,1′-[[(Propane-1,3-diyl)dioxy]bis(11aS)-7-methoxy-2-[[(trifluoromethyl)sulfonyl]oxy]-10-((2-(trimethylsilyl)ethoxy)methyl)-1,10,11,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (8a)

Anhydrous 2,6-lutidine (5.15 mL, 4.74 g, 44.2 mmol) was injected in one portion to a vigorously stirred solution of bis-ketone 7a (6.08 g, 7.1 mmol) in dry DCM (180 mL) at −45° C. (dry ice/acetonitrile cooling bath) under a nitrogen atmosphere. Anhydrous triflic anhydride, taken from a freshly opened ampoule (7.2 mL, 12.08 g, 42.8 mmol), was injected rapidly dropwise, while maintaining the temperature at −40° C. or below. The reaction mixture was allowed to stir at −45° C. for 1 hour at which point TLC (50/50 v/v n-hexane/EtOAc) revealed the complete consumption of starting material. The cold reaction mixture was immediately diluted with DCM (200 mL) and, with vigorous shaking, washed with water (1×100 mL), 5% citric acid solution (1×200 mL) saturated NaHCO₃ (200 mL), brine (100 mL) and dried (MgSO₄). Filtration and evaporation of the solvent in vacuo afforded the crude product which was purified by flash column chromatography (gradient elution: 90:10 v/v n-hexane/EtOAc to 70:30 v/v n-hexane/EtOAc) to afford bis-enol triflate 8a as a yellow foam (5.5 g, 70%).

Analytical Data: [α]²⁴ _(D)=+271° (c=0.18, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ 7.33 (s, 2H), 7.26 (s, 2H), 7.14 (t, 2H, J=1.97 Hz), 5.51 (d, 2H, J=10.1 Hz), 4.76 (d, 2H, J=10.1 Hz), 4.62 (dd, 2H, J=11.0, 3.69 Hz), 4.32-4.23 (m, 4H), 3.94-3.90 (m, 8H), 3.81-3.64 (m, 4H), 3.16 (ddd, 2H, J=16.3, 11.0, 2.36 Hz), 2.43 (p, 2H, J=5.85 Hz), 1.23-0.92 (m, 4H), 0.02 (s, 18H); ¹³C NMR (100 MHz, CDCl₃) δ 167.1, 162.7, 151.9, 148.0, 138.4, 133.6, 120.2, 118.8, 111.9, 107.4, 78.6, 67.5, 65.6, 56.7, 56.3, 30.8, 29.0, 18.4, −1.25; IR (ATR, CHCl₃) 2958, 1690, 1646, 1605, 1517, 1456, 1428, 1360, 1327, 1207, 1136, 1096, 1060, 1022, 938, 913 cm⁻¹; MS (ES⁺) m/z (relative intensity) 1144 ([M+28]^(+.), 100), 1117 ([M+H]^(+.), 48), 1041 (40), 578 (8); HRMS [M+H]^(+.) theoretical C₄₃H₅₄N₄O₁₆Si₂S₂F₆ m/z 1117.2491, found (ES⁺) m/z 1117.2465.

(g) 1,1′-[[(Pentane-1,5-diyl)dioxy]bis(11aS)-7-methoxy-2-[[(trifluoromethyl)sulfonyl]oxy]-10-((2-(trimethylsilyl)ethoxy)methyl)-1,10,11,11 a-tetrahydro-5H-pyrrolo[2,1-c][1,4]-benzodiazepin-5,11-dione] (8b)

Preparation from 7b according to the above method gave the bis-enol triflate as a pale yellow foam (6.14 g, 82%).

Analytical Data: (ES+) m/z (relative intensity) 1146 ([M+H]^(+.), 85).

Example 1

(a) (S)-2-(4-aminophenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(trifluoromethylsulfonyl)-5,11-dioxo-10((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propoxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione (9)

Solid Pd(PPh₃)₄ (20.18 mg, 17.46 mmol) was added to a stirred solution of the triflate 8a (975 mg, 0.87 mmol), 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboralane-2-yl)aniline (172 mg, 0.79 mmol) and Na₂CO₃ (138 mg, 3.98 mol) in toluene (13 mL) EtOH (6.5 mL) and H₂O (6.5 mL). The dark solution was allowed to stir under a nitrogen atmosphere for 24 hours, after which time analysis by TLC (EtOAc) and LC/MS revealed the formation of the desired mono-coupled product and as well as the presence of unreacted starting material. The solvent was removed by rotary evaporation under reduced pressure and the resulting residue partitioned between H₂O (100 mL) and EtOAc (100 mL), after eventual separation of the layers the aqueous phase was extracted again with EtOAc (2×25 mL). The combined organic layers were washed with H₂O (50 mL), brine (60 mL), dried (MgSO₄), filtered and evaporated in vacuo to provide the crude Suzuki product. The crude Suzuki product was subjected to flash chromatography (40%EtOAc/60% Hexane→70% EtOAc, 30% Hexane). Removal of the excess eluent by rotary evaporation under reduced pressure afforded the desired product 9 (399 mg) in 43% yield.

¹H-NMR: (CDCl₃, 400 MHz) δ 7.40 (s, 1H), 7.33 (s, 1H), 7.27 (bs, 3H), 7.24 (d, 2H, J=8.5 Hz), 7.15 (t, 1H, J=2.0 Hz), 6.66 (d, 2H, J=8.5 Hz), 5.52 (d, 2H, J=10.0 Hz), 4.77 (d, 1H, J=10.0 Hz), 4.76 (d, 1H, J=10.0 Hz), 4.62 (dd, 1H, J=3.7, 11.0 Hz), 4.58 (dd, 1H, J=3.4, 10.6 Hz), 4.29 (t, 4H, J=5.6 Hz), 4.00-3.85 (m, 8H), 3.80-3.60 (m, 4H), 3.16 (ddd, 1H, J=2.4, 11.0, 16.3 Hz), 3.11 (ddd, 1H, J=2.2, 10.5, 16.1 Hz), 2.43 (p, 2H, J=5.9 Hz), 1.1-0.9 (m, 4H), 0.2 (s, 18H). ¹³C-NMR: (CDCl₃, 100 MHz) δ 169.8, 168.3, 164.0, 162.7, 153.3, 152.6, 149.28, 149.0, 147.6, 139.6, 134.8, 134.5, 127.9 (methine), 127.5, 125.1, 123.21, 121.5, 120.5 (methine), 120.1 (methine), 116.4 (methine), 113.2 (methine), 108.7 (methine), 79.8 (methylene), 79.6 (methylene), 68.7 (methylene), 68.5 (methylene), 67.0 (methylene), 66.8 (methylene), 58.8 (methine), 58.0 (methine), 57.6 (methoxy), 32.8 (methylene), 32.0 (methylene), 30.3 (methylene), 19.7 (methylene), 0.25 (methyl).

(b) (S)-2-(4-aminophenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-methoxyphenyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propoxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,1aH)-dione (10)

Solid Pd(PPh₃)₄ (10 mg, 8.69 μmol) was added to a stirred solution of the mono-triflate 9 (230 mg, 0.22 mmol) in toluene (3 mL), EtOH (10 mL), with 4-methoxyphenyl boronic acid (43 mg, 0.28 mmol), Na₂CO₃ (37 mg, 0.35 mmol), in H₂O (1.5 mL) at room temperature. The reaction mixture was allowed to stir under a nitrogen atmosphere for 20 h, at which point the reaction was deemed complete as judged by LC/MS and TLC (EtOAc). The solvent was removed by rotary evaporation under reduced pressure in vacuo and the resulting residue partitioned between EtOAc (75 mL) and H₂O (75 mL). The aqueous phase was extracted with EtOAc (3×30 mL) and the combined organic layers washed with H₂O (30 mL), brine (40 mL), dried (MgSO₄), filtered and evaporated to provide the crude product. The crude product was purified by flash chromatography (60% Hexane: 40% EtOAc→80% EtOAc: 20% Hexane) to provide the pure dimer as an orange foam. Removal of the excess eluent under reduced pressure afforded the desired product 10 (434 mg) in 74% yield.

¹H-NMR: (CDCl₃, 400 MHz) δ 7.38 (s, 2H), 7.34 (d, 2H, J=8.8 Hz), 7.30 (bs, 1H), 7.26-7.24 (m, 3H), 7.22 (d, 2H, J=8.5 Hz), 6.86 (d, 2H, J=8.8 Hz), 6.63 (d, 2H, J=8.5 Hz), 5.50 (d, 2H, J=10.0 Hz), 4.75 (d, 1H, J=10.0 Hz), 4.74 (d, 1H, J=10.0 Hz), 4.56 (td, 2H, J=3.3, 10.1 Hz), 4.27 (t, 2H, J=5.7 Hz), 4.00-3.85 (m, 8H), 3.80 (s, 3H), 3.77-3.60 (m, 4H), 3.20-3.00 (m, 2H), 2.42 (p, 2H, J=5.7 Hz), 0.96 (t, 4H, J=8.3 Hz), 0.00 (s, 18H). ¹³C-NMR: (CDCl₃, 100 MHz) δ 169.8, 169.7, 162.9, 162.7, 160.6, 152.7, 152.6, 149.0, 147.5, 134.8, 127.8 (methine), 127.4, 126.8, 125.1, 123.1, 123.0, 121.5 (methine), 120.4 (methine), 116.4 (methine), 115.5 (methine), 113.1 (methine), 108.6 (methine), 79.6 (methylene), 68.5 (methylene), 66.9 (methylene), 58.8 (methine), 57.6 (methoxy), 56.7 (methoxy), 32.8 (methylene), 30.3 (methylene), 19.7 (methylene), 0.0 (methyl).

(c) (S)-2-(4-aminophenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-8-yloxy)propoxy)-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-5(11aH)-one (11)

Fresh LiBH₄ (183 mg, 8.42 mmol) was added to a stirred solution of the SEM-dilactam 10 (428 mg, 0.42 mmol) in THF (5 mL) and EtOH (5 mL) at room temperature. After 10 minutes, delayed vigorous effervescence was observed requiring the reaction vessel to be placed in an ice bath. After removal of the ice bath the mixture was allowed to stir at room temperature for 1 hour. LC/MS analysis at this point revealed total consumption of starting material with very little mono-reduced product. The reaction mixture was poured onto ice (100 mL) and allowed to warm to room temperature with stirring. The aqueous mixture was extracted with DCM (3×30 mL) and the combined organic layers washed with H₂O (20 mL), brine (30 mL) and concentrated in vacuo. The resulting residue was treated with DCM (5 mL), EtOH (14 mL), H₂O (7 mL) and silica gel (10 g). The viscous mixture was allowed to stir at room temperature for 3 days. The mixture was filtered slowly through a sinter funnel and the silica residue washed with 90% CHCl₃: 10% MeOH (˜250 mL) until UV activity faded completely from the eluent. The organic phase was washed with H₂O (50 mL), brine 60 mL), dried (MgSO₄) filtered and evaporated in vacuo to provide the crude material. The crude product was purified by flash chromatography (97% CHCl₃: 3% MeOH) to provide the pure C2/C2′aryl PBD dimer 11 (185 mg) 61% yield.

¹H-NMR: (CDCl₃, 400 MHz) δ 7.88 (d, 1H, J=4.0 Hz), 7.87 (d, 1H, J=4.0 Hz), 7.52 (s, 2H), 7.39 (bs, 1H), 7.37-7.28 (m, 3H), 7.20 (d, 2H, J=8.5 Hz), 6.89 (d, 2H, J=8.8 Hz), 6.87 (s, 1H), 6.86 (s, 1H), 6.67 (d, 2H, J=8.5 Hz), 4.40-4.20 (m, 6H), 3.94 (s, 6H), 3.82 (s, 3H), 3.61-3.50 (m, 2H), 3.40-3.30 (m, 2H), 2.47-2.40 (m, 2H). ¹³C-NMR: (CDCl₃, 100 MHz) δ 162.5 (imine methine), 161.3, 161.1, 159.3, 156.0, 151.1, 148.1, 146.2, 140.3, 126.2 (methine), 123.2, 122.0, 120.5 (methine), 119.4, 115.2 (methine), 114.3 (methine), 111.9 (methine), 111.2 (methine), 65.5 (methylene), 56.2 (methoxy), 55.4 (methoxy), 53.9 (methine), 35.6 (methylene), 28.9 (methylene).

Example 2

(a) (S)-2-(4-aminophenyl)-7-methoxy-8-(5-((S)-7-methoxy-2-(4-methoxyphenyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione (12)

Solid Pd(PPh₃)₄ (32 mg, 27.7 μmol) was added to a stirred solution of the bis-triflate 8b (1.04 g, 0.91 mmol) in toluene (10 mL), EtOH (5 mL), with 4-methoxyphenyl boronic acid (0.202 g, 1.32 mmol), Na₂CO₃ (0.169 g, 1.6 mmol), in H₂O (5 mL) at 30° C. The reaction mixture was allowed to stir under a nitrogen atmosphere for 20 hours. Additional solid 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboralan-2-yl)aniline (0.203 g, 0.93 mmol) and Na₂CO₃ (0.056 g, 0.53 mmol) were added followed by solid Pd(PPh₃)₄ (10 mg, 8.6 μmol). The reaction mixture was allowed to stir under a nitrogen atmosphere for a further 20 hours. LC/MS indicated the formation of desired product. EtOAc (100 mL) and H₂O (100 mL) were added, the aqueous was separated and extracted with EtOAc (3×30 mL). The combined organic layers were washed with H₂O (100 mL), brine (100 mL), dried (MgSO₄), filtered and evaporated to provide a dark brown oil. The oil was dissolved in DCM and loaded onto a 10 g SCX-2 cartridge pre-equilibrated with DCM (1 vol). The cartridge was washed with DCM (3 vol), MeOH (3 vol) and the crude product eluted with 2M NH₃ in MeOH (2 vol). Flash chromatography (50% n-hexane: 50% EtOAc→20% n-hexane: 80% EtOAc) provided the pure dimer 12 as a yellow foam (0.16 g, 34%).

Analytical Data: [α]²³ _(D)=+388° (c=0.22, CHCl₃); ¹H-NMR: (CDCl₃, 400 MHz) δ 7.39 (s, 2H), 7.35 (d, 2H, J 12.8 Hz), 7.32 (bs, 1H), 7.26-7.23 (m, 5H), 6.89 (d, 2H, J=8.8 Hz), 6.66 (d, 2H, J=8.5 Hz), 5.55 (d, 2H, J=10.0 Hz), 4.73 (d, 1H, J=10.0 Hz), 4.72 (d, 1H, J=10.0 Hz), 4.62 (td, 2H, J=3.2, 10.4 Hz), 4.15-4.05 (m, 4H), 4.00-3.85 (m, 8H), 3.82 (s, 3H), 3.77-3.63 (m, 4H), 3.20-3.05 (m, 2H), 2.05-1.95 (m, 4H), 1.75-1.67 (m, 2H) 1.01-0.95 (m, 4H), 0.03 (s, 18H); MS (ES⁺) m/z (relative intensity) 1047 ([M+H]^(+.), 45).

(b) (S)-2-(4-aminophenyl)-7-methoxy-8-(5-((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-8-yloxy)pentyloxy)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5(11aH)-one (13)

Fresh LiBH₄ (66 mg, 3.04 mmol) was added to a stirred solution of the SEM-dilactam 12 (428 mg, 0.42 mmol) in THF (3 mL) and EtOH (3 mL) at 0° C. (ice bath). The ice bath was removed and the reaction mixture was allowed to reach room temperature (vigorous effervescence). After 2 hours LC/MS analysis indicated the complete consumption of starting material. The reaction mixture was poured onto ice (50 mL) and allowed to warm to room temperature with stirring. The aqueous mixture was extracted with DCM (3×50 mL) and the combined organic layers washed with H₂O (50 mL), brine (50 mL), dried (MgSO₄) and concentrated in vacuo. The resulting residue was treated with DCM (2 mL), EtOH (5 mL), H₂O (2.5 mL) and silica gel (3.7 g). The viscous mixture was allowed to stir at room temperature for 3 days. The mixture was filtered through a sinter funnel and the silica residue washed with 90% CHCl₃: 10% MeOH (˜250 mL) until UV activity faded completely from the eluent. The organic phase was dried (MgSO₄) filtered and evaporated in vacuo to provide the crude material. The crude product was purified by flash chromatography (99.5% CHCl₃: 0.5% MeOH to 97.5% CHCl₃: 2.5% MeOH in 0.5% increments)) to provide the pure C2/C2′aryl PBD dimer 13 (59 mg, 52%).

Analytical Data: [α]²⁸ _(D)=+760° (c=0.14, CHCl₃); ¹H NMR (400 MHz, CDCl₃) δ 7.89 (d, 1H, J=4.0 Hz), 7.87 (d, 1H, J=4.0 Hz), 7.52 (s, 2H), 7.39 (bs, 1H), 7.37-7.28 (m, 3H), 7.22 (d, 2H, J=8.4 Hz), 6.91 (d, 2H, J=8.8 Hz), 6.815 (s, 1H), 6.81 (s, 1H), 6.68 (d, 2H, J=8.4 Hz), 4.45-4.35 (m, 2H), 4.2-4.0 (m, 4H), 3.94 (s, 6H), 3.85-3.7 (s, 3H), 3.65-3.50 (m, 2H), 3.45-3.3 (m, 2H), 2.05-1.9 (m, 4H), 1.75-1.65 (m, 2H): MS (ES⁺) (relative intensity) 754.6 ([M+H]^(+.), 100), (ES⁻) (relative intensity) 752.5 ([M−H]^(−.), 100).

Example 3

(a) (S)-2-(thien-2-yl)-7-methoxy-8-(3-((S)-7-methoxy-2-(trifluoromethanesulfonyloxy)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propyloxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione (14)

Solid Pd(PPh₃)₄ (41 mg, 0.036 mmol) was added to a stirred solution of the bis-triflate 8a (1 g, 0.9 mmol) in toluene (10 mL), EtOH (5 mL), with thien-2-yl boronic acid (149 mg, 1.16 mmol), Na₂CO₃ (152 mg, 1.43 mmol), in H₂O (5 mL). The reaction mixture was allowed to stir under a nitrogen atmosphere overnight at room temperature. The solvent was removed by evaporation in vacuo and the resulting residue partitioned between H₂O (100 mL) and EtOAc (100 mL). The aqueous layer was extracted with EtOAc (2×30 mL) and the combined organic layers washed with H₂O (50 mL), brine (50 mL) dried (MgSO₄), filtered and evaporated in vacuo to provide the crude product which was purified by flash chromatography (80 hexane: 20 EtOAc→50 hexane: 50 EtOAc) to provide the dimer 14 (188 mg, 20%) yield

Analytical data: LC-MS RT 4.27 mins, 1051 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.36 (s, 1H), 7.31 (bs, 1H), 7.27 (bs, 1H), 7.26-7.23 (m, 2H), 7.22-7.17 (m, 1H), 7.12 (bs, 1H), 7.02-6.96 (m, 2H), 5.50 (d, J=10.0 Hz, 2H), 7.75 (d, J=10.0 Hz, 2H), 4.65-4.55 (m, 2H), 4.37-4.13 (m, 4H), 4.00-3.85 (m, 8H), 3.8-3.6 (m, 4H), 3.20-3.10 (m, 2H), 2.50-2.35 (m, 2H), 1.0-0.9 (m, 4H), 0 (s, 18H).

(b) (S)-2-(thien-2-yl)-7-methoxy-8-(3-((S)-7-methoxy-2-(trifluoromethanesulfonyloxy)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-5,11(10H,11aH)-dione (15)

Solid Pd(PPh₃)₄ (7.66 mg, 6.63 μmol) was added to a stirred, cloudy solution of 14 (174 mg, 0.17 mmol), Na₂CO₃ (28 mg, 0.22 mmol) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboralan-2-yl)aniline (47 mg, 0.22 mmol) in toluene (2-5 mL), EtOH (1.25 mL) and H₂O (125 mL) at room temperature. The reaction mixture was allowed to stir under a atmosphere for 24 hours at which point the reaction was deemed complete by LC/MS major peak (@3.97 min, FW=1016, M+Na) and TLC (EtOAc). The solvent was removed by evaporation in vacuo and the resulting residue partitioned between EtOAc (60 mL) and H₂O (30 mL). The layers were separated and the organic phase was washed with H₂O) (20 mL), brine (30 mL) dried (MgSO₄) filtered and evaporated in vacuo to provide the crude product 123 mg, 75% yield.

Analytical data: LC-MS RT 3.98 mins, 100% area, 994 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.40 (d, J=5.3 Hz, 2H), 7.30 (t, J=1.70 Hz, 1H), 7.29-7.27 (m, 3H), 7.25 (d, J=8.5 Hz, 2H), 7.21 (dd, J=1.4, 4.73 Hz, 1H), 7.03-6.97 (m, 2H), 6.66 (d, J=8.5 Hz, 2H), 5.52 (d, J=10.0 Hz, 2H), 4.78 (d, J=10.0 Hz, 1H), 4.77 (d, J=10.0 Hz, 1H), 4.62 (dd, J=3.4, 10.5 Hz, 1H), 4.59 (dd, J=3.40, 10.6 Hz, 1H), 4.30 (t, J=5.85 Hz, 4H), 3.85-4.03 (m, 8H), 3.84-3.64 (m, 6H), 3.18 (ddd, J=2.2, 10.5, 16.0 Hz, 1H), 3.11 (ddd, J=2.2, 10.5, 16.0 Hz, 1H), 2.44 (p, J=5.85 Hz, 2H), 0.98 (t, J=1.5 Hz, 4H), 0 (s, 18H).

(c) (S)-2-(thien-2-yl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-aminophenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-8-yloxy)propyloxy)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5(11aH)-one (16)

Fresh LiBH₄ (47 mg, 2.22 mmol) was added to a stirred solution of the SEM-dilactam 15 (110 mg, 0.11 mmol) in dry THF (3 mL) and EtOH (3 mL) at 0° C. (ice bath). The ice bath was removed and the reaction mixture stirred under a N₂ atmosphere for 1 hour. Analysis of the reaction by LC/MS analysis revealed significant formation of the desired product (Pk @2.57 min) (I=69.32), FW=702, M+H) and half-imine. The reaction mixture was allowed to stir for a further 1 hour after which time no further reaction progress was observed by LC/MS. The reaction mixture was poured onto ice, stirred and allowed to warm to room temperature. Following partition between DCM (50 mL) and water (50 mL), the aqueous phase was extracted with DCM (3×20 mL). The combined organic layers were washed with H₂O (50 mL), brine (50 mL) and the solvent removed by evaporation in vacuo under reduced pressure.

The resulting residue was dissolved in DCM (5 mL), EtOH (15 mL) and H₂O (7 mL) then treated with silica gel (5 g). The reaction was allowed to stir at room temperature for 48 h. The silica was removed by filtration through a sinter funnel and the residue rinsed with 90:10 CHCl₃:MeOH (100 mL). H₂O (50 mL) was added to the filtrate and the layers were separated (after shaking). The aqueous layer was extracted with CHCl₃ (2×30 mL) and H₂O (50 mL), brine (50 mL), dried (MgSO₄) filtered and evaporated in vacuo to provide the crude product. Flash chromatography (CHCl₃→98% CHCl₃: 2% MeOH) afforded the product (41 mg, 53%).

Analytical data: LC-MS RT 2.55 mins, 702 (M+H)

Example 4

(a) (S)-2-(4-methoxyphenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(trifluoromethylsulphonyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-C][1,4]benzodiazepin-8-yloxy)propyloxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-5,11(10H,11aH)-dione (17)

Solid 4-methoxybenzeneboronic acid (0.388 g, 2.55 mmol) was added to a solution of the SEM protected his triflate (8a) (3.0 g, 2.69 mmol), sodium carbonate (426 mg, 4.02 mmol) and palladium tetrakis triphenylphosphine (0.08 mmol) in toluene (54.8 mL), ethanol (27 mL) and water (27 mL). The reaction mixture was allowed to stir at room temperature for 3 hours. The reaction mixture was then partitioned between ethyl acetate and water. The organic layer was washed with water and brine and dried over magnesium sulphate. Excess solvent was removed by rotary evaporation under reduced pressure and the resulting residue was subjected to flash column chromatography (silica gel; gradient elution EtOAc/hexane 30/70→35/65→40/60→45/55) to remove unreacted bis-triflate (0.6 g). Removal of excess eluent from selected fractions afforded the 4-methoxyphenyl coupled product (1.27 g, 1.18 mmol, 41%).

LC-MS RT 4.30 mins, 1076 (M+H); ¹H-NMR (400 MHZ, CDCl₃) 7.41 (s, 1H), 7.39 (d, J=8.8 Hz, 2H), 7.35 (s, 1H), 7.34 (bs, 1H), 7.29 (s, 1H), 7.16 (t, J=1.9 Hz, 1H), 6.90 (d, J=8.8 Hz, 2H), 5.53 (d, J=10.0 Hz, 2H), 4.79 (d, J=10.0 Hz, 1H), 4.78 (d, J=10.0 Hz, 1H), 4.66-4.60 (m, 2H), 4.30 (t, J=5.7 Hz, 4H), 4.0-3.94 (m, 2H), 3.93 (s, 3H), 3.92 (s, 3H), 3.84 (s, 3H), 3.83-3.60 (m, 4H), 3.22-3.10 (m, 2H), 2.45 (t, J=5.9 Hz, 2H), 1.05-0.94 (m, 4H), 0 (s, 18H).

(b) (S)-2-(3-aminophenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-methoxyphenyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propyloxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-5,11(10H,11aH)-dione (18)

Solid 3-aminobenzeneboronic acid (0.143 g, 0.92 mmol) was added to a solution of the mono triflate (17) (0.619 g, 0.58 mmol), sodium carbonate (195 mg, 1.84 mmol) and palladium tetrakis triphenylphosphine (26.6 mg, 0.023 mmol) in toluene (10 mL), ethanol (5 mL) and water (5 mL). The reaction mixture was allowed to stir at room temperature for overnight at 30° C. The reaction mixture was then partitioned between ethyl acetate and water. The organic layer was washed with water and brine and dried over magnesium sulphate. Excess solvent was removed by rotary evaporation under reduced pressure and the resulting residue was subjected to flash column chromatography (silica gel; gradient elution EtOAdhexane 70/30→85/15). Removal of excess eluent from selected fractions afforded the desired product (0.502 g, 0.49 mmol, 85%).

LC-MS RT 4.02 mins, 1019 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.38-7.35 (m, 4H), 7.33 (bs, 1H), 7.30 (bs, 1H), 7.25 (s, 2H), 7.10 (t, J=7.8 Hz, 1H), 6.88-6.80 (m, 3H), 6.72 (bs, 1H), 6.57 (dd, J=7.9, 1.8 Hz, 1H), 5.50 (d, J=10.0 Hz, 2H), 4.75 (d, 10.0 Hz, 2H), 4.58 (dd, J=10.6, 3.3 Hz, 2H), 4.27 (t, J=5.8 Hz, 4H), 3.95-3.91 (m, 2H), 3.90 (s, 6H), 3.80 (s, 3H), 3.77-3.60 (m. 6H), 3.15-3.05 (m, 2H), 2.41 (p, J=5.8 Hz, 2H), 0.95 (t, =8.25 Hz, 4H), 0 (s, 18H).

(c) (S)-2-(3-aminophenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-8-yloxy)propyloxy)-1H-pyrrolo[2,1-c] [1,4]benzodiazepine-5(11aH)-one (19)

A solution of superhydride (0.56 mL, 0.56 mmol, 1.0 M in THF) was added dropwise to a solution of the SEM dilactam (18)(0.271 g, 0.27 mmol) in dry THF (10 mL) at −78° C. under a nitrogen atmosphere. After 1 hr a further aliquot of superhydride solution (0.13 ml, 0.13 mmol) was added and the reaction mixture was allowed to stir for another 0.5 hr, at which time LC-MS indicated that reduction was complete. The reaction mixture was diluted with water and allowed to warm to room temperature. The reaction mixture was partitioned between chloroform and water, the layers were separated and the aqueous layer extracted with additional chloroform (emulsions). Finally the combined organic phase was washed with brine and dried over magnesium sulphate. The reduced product was dissolved in methanol, chloroform and water and allowed to stir in the presence of silica gel for 72 hours The crude product was subjected to flash column chromatography (methanol/chloroform gradient) to afford the desired imine product (150 mg, 0.21 mmol, 77%) after removal of excess eluent from selected fractions.

LC-MS RT 2.63 mins, 97% area, 726 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.85 (d, J=3.9 Hz, 1H), 7.84 (d, J=3.9 Hz, 1H), 7.50 (s, 1H), 7.49 (s, 1H), 7.42 (s, 1H), 7.36 (s, 1H), 7.32 (d, J=7.3 Hz, 2H), 7.11 (t, (d, J=7.8 Hz, 1H), 6.90-6.80 (m, 4H), 6.77 (d, J=7.9 Hz, 1H), 4.40-4.20 (m, 6H), 3.92 (s, 6H), 3.80 (s, 3H), 3.60-3.27 (m, 6H), 2.48-2.29 (m, 2H)

Example 5

(a) (11S11aS)-2,2,2-trichloroethyl 11-(tert-butyldimethylsilyloxy)-8-(5-((11S,11aS)-11-(tert-butyldimethylsilyloxy)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-10-((2,2,2-trichloroethoxy)carbonyl)-5,10,11,11a-tetrahydro-1H-pyrrolo [2,1-c][1,4] benzodiazepin-8-yloxy)pentyloxy)-7-methoxy-5-oxo-2-(trifluoromethylsulfonyloxy)-11,11a-dihydro-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate 21

Solid 4-methoxybenzeneboronic acid (59 mg, 0.39 mmol) was added to a solution of the Troc protected bis triflate (Compound 44, WO 2006/111759) (600 mg, 0.41 mmol), sodium carbonate (65 mg, 0.61 mmoml) and palladium tetrakis triphenylphosphine (0.012 mmol) in toluene (10.8 mL), ethanol (5.4 mL) and water (5.4 mL). The reaction mixture was allowed to stir at room temperature overnight. The reaction mixture was then partitioned between ethylacetate and water. The organic layer was washed with water and brine and dried over magnesium sulphate. Excess solvent was removed by rotary evaporation under reduced pressure and the resulting residue was subjected to flash column chromatography (silica gel; gradient elution EtOAc/hexane 20/80→30/70→40/60→60/40) to remove unreacted bis-triflate. Removal of excess eluent from selected fractions afforded the 4-methoxyphenyl coupled product (261 mg, 0.18 mmol, 46%).

LC-MS RT 4.17 mins, 1427 (M+H); ¹H-NMR (400 MHZ, CDCl₃) 7.38 (s, 1H), 7.33 (s, 1H), 7.31 (s, 1H), 7.30 (s, 1H), 7.25 (s, 1H), 7.20 (bs, 1H), 6.92 (d, J=8.6 Hz, 2H), 6.77 (d, J=8.7 Hz, 2H), 6.0-5.90 (m, 2H), 5.25 (d, J=12.0 Hz, 1H), 5.24 (d, J=12.0 Hz, 1H), 4.24 (d, J=12.0 Hz, 1H), 4.22 (d, J=12.0 Hz, 1H), 4.18-4.08 (m, 2H), 4.07-3.89 (m, 10H), 3.81 (s, 3H), 3.44-3.25 (m, 2H), 2.85 (d, J=16.6 Hz, 2H), 2.05-1.90 (m, 4H), 1.76-1.64 (m, 2H), 0.93 (s, 9H), 0.90 (s, 9H), 0.30 (s, 6H), 0.26 (s, 6H).

(b) (11S,11aS)-2,2,2-trichloroethyl 11-(tert-butyldimethylsilyloxy)-8-(5-((11S,11aS)-11-(tert-butyldimethylsilyloxy)-2-(4-hydroxyphenyl)-7-methoxy-5-oxo-10-((2,2,2-trichloroethoxy)carbonyl-5,10,11,11a-tetrahydro-1H-pyrrolo [2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-11,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate 22

The Suzuki coupling procedure described in step (a) was applied to the synthesis of Compound 21. Compound 20 (62.5 mg 0.044 mmol,) was treated with 1 equivalent of 4-hydroxybenzeneboronic acid (10 mg) at 30° C. overnight to afford the desired compound after filtration through a pad of silica gel. (40 mg, 0.029 mmol, 66% yield). The compound was used directly in the subsequent step

LC-MS RT 4.27 mins, 1371 (M+H)

(c) (S)-2-(4-hydroxyphenyl)-7-methoxy-8-(5-((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5(11aH)-one 23

Cadmium/lead couple (100 mg, Q Dong et al. Tetrahedron Letters vol 36, issue 32, 5681-5682, 1995) was added to a solution of 21 (40 mg, 0.029 mmol) in THF (1 mL) and ammonium acetate (1N, 1 mL) and the reaction mixture was allowed to stir for 1 hour. The reaction mixture was partitioned between chloroform and water, the phases separated and the aqueous phase extracted with chloroform. The combined organic layers were washed with brine and dried over magnesium sulphate. Rotary evaporation under reduced pressure yielded the crude product which was subjected to column chromatography (silica gel, 0→4% MeOH/CHCl₃). Removal of excess eluent by rotary evaporation under reduced pressure afforded the desired imine product (17 mg 0.023 mmol 79%).

LC-MS RT 2.20 mins, 755 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.89 (d, J=3.94 Hz, 1H), 7.89 (d, J=4.00 Hz, 1H), 7.53 (s, 1H), 7.52 (s, 1H), 7.38 (d, J=8.7 Hz, 2H), 7.33 (d, J=8.6 Hz, 2H), 7.28 (s, 1H), 6.90 (d, J=8.7 Hz, 2H), 6.84 (d, J=8.6 Hz, 2H), 6.82 (s, 1H), 6.81 (s, 1H), 5.68 (bs, 1H), 4.50-4.30 (m, 2H), 4.22-4.00 (m, 4H), 3.93 (s, 6H), 3.82 (s, 3H), 3.69-3.45 (m, 2H), 3.44-3.28 (m, 2H), 2.64-1.88 (m, 4H), 1.77-1.62 (m, 2H).

Example 6

(a) (11S,11aS)-2,2,2-trichloroethyl 11-(tert-butyldimethylsilyloxy)-8-(5-((11S,11aS)-11-(tert-butyldimethylsilyloxy)-2-(4-formylphenyl)-7-methoxy-5-oxo-10-((2,2,2-trichloroethoxy)carbonyl)-5,10,11,11 a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-11,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate 24

The Suzuki coupling procedure described in Example 5, step (a), was applied to the synthesis of Compound 24. Compound 21 (62.5 mg, 0.044 mmol) was treated with 1 equivalent of 4-formylbenzeneboronic acid (10.5 mg) at room temperature overnight to afford the desired compound after filtration through a pad of silica gel (45 mg, 0.033 mmol, 75% yield). The compound was used directly in the subsequent step.

LC-MS RT 4.42 mins, 1383 (M+H)

(b) 4-((S)-7-methoxy-8-(5-((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin)-8-yloxy)pentyloxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-2-yl)benzaldehyde 25

Compound 24 was deprotected by the method described in Example 5, step (c), to yield the desired compound (18 mg, 0.023 mmol, 79%).

LC-MS RT 3.18 mins, 768 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 9.98 (s, 1H), 7.91 (d, J=3.90 Hz, 1H), 7.90-7.80 (m, 3H), 7.68 (s, 1H), 7.60-7.45 (m, 4H), 7.39 (s, 1H), 7.33 (d, J=8.7 Hz, 1H), 6.90 (d, J=8.7 Hz, 2H), 6.83 (s, 1H), 6.82 (s, 1H), 4.55-4.44 (m, 1H), 4.43-4.36 (m, 1H), 4.23-4.00 (m, 4H), 3.95 (s, 3H), 3.94 (s, 3H), 3.82 (s, 3H), 3.66-3.51 (m, 2H), 3.50-3.34 (m, 2H), 2.05-1.87 (m, 4H), 1.76-164 (m, 2H).

Example 7

(a) (11S,11aS)-2,2,2-trichloroethyl 2-(3-aminophenyl)-11-(tert-butyldimethylsilyloxy)-8-(5-((11S,11aS)-11-(tert-butyldimethylsilyloxy)-7-methoxy-5-oxo-10-((2,2,2-trichloroethoxy)carbonyl)-2-(trifluoromethylsulphonyloxy)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-7-methoxy-5-oxo-11,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate 26

The Suzuki coupling procedure described in Example 5, step (a), was applied to the synthesis of Compound 26, using 3-aminobenzeneboronic acid to afford the desired compound in 41% yield (230 mg, 0.163 mmol)

LC-MS RT 4.28 mins, 1411 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.44 (bs, 1H), 7.29 (s, 1H), 7.25 (s, 1H), 7.20 (s, 1H), 7.16 (t, J=7.9 Hz, 1H), 6.84-6.73 (m, 3H), 6.70 (bs, 1H), 6.62 (dd, J=7.9, 1.7 Hz, 1H), 6.66-6.58 (m, 2H), 5.25 (d, J=12.0 Hz, 1H), 5.24 (d, J=12.0 Hz, 1H), 4.24 (d, J=12.0 Hz, 1H), 4.22 (d, J=12.0 Hz, 1H),4.17 4.07 (m, 2H), 4.08-3.89 (m, 10H), 3.43-3.28 (m, 2H), 2.85 (d, J=1.65 Hz, 2H), 2.07-1.90 (m, 4H), 1.78-1.63 (m, 2H), 0.94 (s, 9H), 0.90 (s, 9H), 0.30 (s, 6H), 0.27 (s, 6H).

(b) (11S,11aS)-2,2,2-trichloroethyl 2-(3-aminophenyl)-11-(tert-butyldimethylsilyloxy)-8-(5-((11S,11aS)-11-(tert-butyldimethylsilyloxy)-2-(4-(3-(dimethylamino)propoxy)phenyl-7-methoxy-5-oxo-10-((2,2,2-trichloroethoxy)carbonyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-7-methoxy-5-oxo-11,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate 27

Solid 4-[3-(dimethylamino)propoxybenzeneboronic acid pinacol ester (25 mg, 0.082 mmol) was added to a solution of 26 (73 mg, 0.052 mmol mmol), sodium carbonate (18 mg, 0.17 mmol) and palladium tetrakis triphenylphosphine (3 mg) in toluene (1 mL), ethanol (0.5 mL) and water (0.5 mL). The reaction mixture was allowed to stir at room temperature over night. The reaction mixture was then partitioned between ethyl acetate and water. The organic layer was washed with water and brine and dried over magnesium sulphate. Excess solvent was removed by rotary evaporation under reduced pressure and the resulting residue was eluted through a plug of silica gel with chloroform/methanol. Removal of excess eluent from selected fractions afforded the 4-methoxyphenyl coupled product (50 mg, 0.035 mmol, 67%).

LC-MS RT 4.12 mins, 1440 (M+H)

(c) (S)-2-(3-aminophenyl)-8-(5-((S)-2-(4-(3-(dimethylamino)propoxy)phenyl)-7-methoxy-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-8-yloxy)pentyloxy)-7-methoxy-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5(11aH)-one 28

Compound 27 was deprotected by the method described in Example 5, step (c), to yield the desired compound. The reaction mixture was partitioned between DCM and aqueous sodium hydrogen carbonate (emulsion) and the crude product purified by gradient column chromatography on silica gel (5% methanol chloroform→35% methanol/chloroform) to afford the desired unsymmetrical PBD imine (50 mg, 0.018 mmol, 58%)

LC-MS RT 2.55 mins, 826 (M+H); ¹H-NMR (400 MHZ, CDCl₃) δ 7.92-7.82 (m, 2H), 7.52 (bs, 2H), 7.45 (bs, 1H), 7.39 (bs, 1H), 7.31 (d, J=8.6 Hz, 2H), 7.14 (t, J=7.8 Hz, 1H), 6.89 (d, J=8.6 Hz, 2H), 6.85-6.75 (m, 3H), 6.72 (bs, 1H), 6.60 (d, J=8.0 Hz, 1H), 4.46-4.33 (m, 2H), 4.21-3.98 (m, 6H), 3.94 (s, 6H). 3.63-3.50 (m, 2H), 3.43-3.29 (m, 2H), 2.64-2.48 (m, 2H), 2.34 (s, 6H), 2.10-1.89 (m, 6H), 1.57 (m, 2H).

Example 8

(a) (11S,11aS)-2,2,2-trichlomethyl 2-(3-aminophenyl)-11-(tert-butyldimethylsilyloxy)-8-(5-((11S,11aS)-11-(tert-butyldimethylsilyloxy)-7-methoxy-2-(4-(4-methylpiperazin-1-yl)phenyl)-5-oxo-10-((2,2,2-trichloroethoxy)carbonyl)-5,10,11,11a-tefrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-7-methoxy-5-oxo-11,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-10(5H)-carboxylate 29

The method of Example 7, step (b), was performed to afford the desired product (58 mg, 0.040 mmol, 78%) after filtration through a plug of silica gel (with ⅓ methanol/chloroform) and removal of excess solvent by rotary evaporation under reduced pressure.

LC-MS RT 4.08 mins, 1439 (M+H)

(b) (S)-2-(3-aminophenyl)-7-methoxy-8-(5-((S)-7-methoxy-2-(4-(4-methylpiperazin-1-yl)phenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)pentyloxy)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5(11aH)-one 30

The method for Example 7, step (c) was used to deprotect compound 29. The crude product was purified by silica gel gradient chromatography (2% methanol chloroform, 35% methanol/chloroform) to afford the desired unsymmetrical PBD imine (18 mg, 0.022 mmol, 59%)

LC-MS RT 2.52 mins, 823 (M+H); ¹H-NMR (400 MHZ, CDCl₃) 7.80 (d, J=3.8Hz, 2H), 7.45 (s, 2H), 7.38 (s, 1H), 7.30 (s, 1H), 7.23 (d, J=8.6Hz, 2H), 7.07 (t, J=7.8 Hz, 1H), 6.83 (d, J=8.6 Hz, 2H), 6.79-6.89 (m, 3H), 6.65 (s, 1H), 6.54 (d, J=7.9 Hz, 1H), 4.40-4.24 (m, 2H), 4.15-3.93 (m, 4H), 3.87 (s, 6H), 3.56-3.42 (m, 2H), 3.37-3.23 (m, 2H), 3.22-3.08 (m, 4H), 2.61-2.41 (m, 4H), 2.29 (s, 3H), 1.98-1.80 (m, 4H), 1.67-1.54 (m, 2H).

Example 9

(a) (S)-2-(4-(aminomethyl)phenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-methoxyphenyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propyloxy)-10-((2-(trimethylsifyl)ethoxy)methyl)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione 31

Solid 4-aminomethylbenzeneboronic acid hydrochloride (0.111 g, 0.59 mmol) was added to a solution of 17 (0.394 g, 0.37 mmol), sodium carbonate (175 mg, 1.654 mmol) and palladium tetrakis triphenylphosphine (28.0 mg, 0.024 mmol) in toluene (10 mL), ethanol (5 mL) and water (5 mL). The reaction mixture was allowed to stir overnight at 30° C. The following day the reaction mixture was heated for a further 3 hours at 70° C. The reaction mixture was then partitioned between ethyl acetate and water. The organic layer was washed with water and brine and dried over magnesium sulphate. Excess solvent was removed by rotary evaporation under reduced pressure and the resulting residue was subjected to flash column chromatography (silica gel; gradient elution EtOAc/hexane 2/98→15/85). Removal of excess eluent from selected fractions afforded the desired product (0.230 mg, 0.22 mmol, 61%).

LC-MS RT 3.63 mins, 1034 (M+2H); ¹H-NMR (400 MHz, DMSO d₆) δ 11.7 (s, 2H), 7.52 (d, J=8.2 Hz, 2H), 7.48 (d, J=8.7 Hz, 2H), 7.40 (s, 1H), 7.50 (d, J=8.1 Hz, 2H),7.38-7.19 (m, 5H) 6.93 (d, J=8.7 Hz, 2H), 5.40 (d, J=2.13 Hz, 1H), 5.38 (d, J=2.12 Hz, 1H), 5.32 (d, J=10.6 Hz, 2H), 5.25 (d, J=10.6 Hz, 2H), 4.87-4.72 (m, 2H), 4.35-4.15 (m, 4H), 3.85 (s, 6H), 3.79 (s, 3H), 3.73-3.56 (m, 2H), 3.55-3.39 (m, 4H), 3.22-3.02 (m, 2H), 2.39-2.23 (m, 2H), 0.94-0.67 (m, 4H), -0.06 (s, 18H).

(b) (S)-2-(4-(aminomethyl)phenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-8-yloxy)propyloxy)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5(11aH)-one 32

Compound 31 was deprotected following the method of Example 1, step (c). The crude product was purified by gradient column chromatography (5/95→30/70 MeOH/CHCl₃) to afford the product as a mixture of imine and carbinolamine methyl ethers.

LC-MS RT 2.58 mins, 740 (M+H).

Example 10

(S)-2-(4-aminophenyl)-7-methoxy-11(S)-sulpho-8-(3-((S)-7-methoxy-11(S)-sulpho-2-(4-methoxyphenyl)-5-oxo-5,10,11,11a -tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propyloxy)-1H-pyrrolo[2,1-c][1,4,]benzodiazepine-5(11aH)-one disodium salt 33

Sodium bisulphite (8.5 mg, 3.1 eq) was added to a stirred suspension of bis-imine 11 (20 mg, 0.036 mmol) in isopropanol (4 mL) and water (2 mL). The reaction mixture was allowed to stir vigorously and eventually became clear (c. 1 hour). The reaction mixture was transferred to a funnel and filtered through a cotton wall (and then washed with 2 mL water). The filtrate was flash frozen (liquid and to bath) and lyophilized to afford the desired product 33 in quantitative yield.

LC-MS RT 11.77 mins, 727.2 (M+H) (Mass of parent compound, bisulphite adducts unstable in mass spectrometer); ¹H-NMR (400 MHz, CDCl₃) δ 7.66-7.55 (m, 5H), 7.43 (s, 1H), 7.39 (d, J=8.66 Hz, 2H), 7.06 (m, 2H), 6.93 (d, J=8.84 Hz, 2H), 6.54 (m, 2H), 5.29-5.21 (m, 2H), 4.32-4.28 (m, 2H), 4.14-4.20 (m, 4H), 3.96-3.83 (m, 2H), 3.77 (s, 3H), 3.73 (m, 6H), 3.52-3.43 (m, 2H), 3.30-3.08 (m, 2H), 2.24-2.21 (m, 2H).

Example 11

(a) (S)-2-(2-aminophenyl)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-10-((2-(trimethylsilfyl)ethoxy)methyl)-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione (103)

A catalytic amount of tetrakistriphenylphosphinepalladium (0) (11.2 mg) was added to a mixture of the mono triflate 17 (380 mg), the pinnacol ester of 2-aminophenylboronic acid (124 mg) and sodium carbonate (120 mg) in ethanol (5 mL), toluene (5mL) and water (5 mL). The reaction mixture was allowed to stir over night at room temperature and at 40° C. until the reaction was complete (c. 2 hr). The reaction mixture was diluted with ethyl acetate and the organic layer was washed with water and brine. The ethyl acetate solution was dried over magnesium sulphate and filtered under vacuum. Removal of ethyl acetate by rotary evaporation under reduced pressure afforded the crude product which was subjected to flash chromatography (silica gel, ethyl acetate/hexane). Pure fractions were collected and combined. Removal of excess eluent by rotary evaporation under reduced pressure afforded the pure product 103 (330 mg, 86% yield). LC/MS RT: 4.17 min, ES⁺ 1018.48.

(b) (S)-2-(2-aminophenyl)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-pyrrolo[2,1-c][1,4]benzodiazepin-5(11aH)-one (104)

A solution of Superhydride in dry tetrahydrofuran (1.0 M, 4.4 eq.) was added to a solution of the 2-analino compound 103 (300 mg) in dry tetrahydrofuran (5 mL) at −78° C. under an inert atmosphere. As reduction was proceeding slowly an aliquot of lithium borohydride (20 eq.) was added and the reaction mixture was allowed to return to room temperature. Water/ice was added to the reaction mixture to quench unreacted hydrides and the reaction was diluted with dichloromethane. The organic layer was washed sequentially with water (twice), citric acid and brine. Excess dichloromethane was removed by rotary evaporation under reduced pressure and the residue was redissolve in ethanol and water and treated with silica gel for 96 hours. The reaction mixture was vacuum filtered and the filtrate evaporated to dryness. The residue was subjected to flash column chromatography (silica gel, gradient chloroform/methanol). Pure fractions were collected and combined and excess eluent was removed by rotary evaporation under educed pressure to afford the pure product 104 (30 mg, 14% yield). LC/MS RT: 2.90 min, ES+726.09.

Example 12 Determination of In Vitro Cytotoxicity of Representative PBD Compounds

K562 Assay

K562 human chronic myeloid leukaemia cells were maintained in RPM1 1640 medium supplemented with 10% fetal calf serum and 2 mM glutamine at 37° C. in a humidified atmosphere containing 5% CO₂ and were incubated with a specified dose of drug for 1 hour or 96 hours at 37° C. in the dark. The incubation was terminated by centrifugation (5 min, 300 g) and the cells were washed once with drug-free medium. Following the appropriate drug treatment, the cells were transferred to 96-well microtiter plates (10⁴ cells per well, 8 wells per sample). Plates were then kept in the dark at 37° C. in a humidified atmosphere containing 5% CO₂. The assay is based on the ability of viable cells to reduce a yellow soluble tetrazolium salt, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT, Aldrich-Sigma), to an insoluble purple formazan precipitate. Following incubation of the plates for 4 days (to allow control cells to increase in number by approximately 10 fold), 20 μL of MTT solution (5 mg/mL in phosphate-buffered saline) was added to each well and the plates further incubated for 5 h. The plates were then centrifuged for 5 min at 300 g and the bulk of the medium pipetted from the cell pellet leaving 10-20 μL per well. DMSO (200 μL) was added to each well and the samples agitated to ensure complete mixing. The optical density was then read at a wavelength of 550 nm on a Titertek Multiscan ELISA plate reader, and a dose-response curve was constructed. For each curve, an IC₅₀ value was read as the dose required to reduce the final optical density to 50% of the control value.

Compound 13 has an IC₅₀ of 30 pM in this assay.

A2780 Assay

The A2780 parental cell line was grown in Dulbecco's Modified Eagles' Media (DMEM) containing ˜10% Foetal Calf Serum (FCS) and ˜1% 200 mM L-Glutamine solution and grown in Corning Cellbind 75 cm²flasks.

A 190 μl cell suspension was added (at 1×10⁴) to each well of columns 2 to 11 of a 96 well plate (Nuns 96F flat bottom TC plate). 190 μl of media was added to each well of columns 1 and 12. The media was Dulbecco's Modified Eagles' Media (DMEM) (which included ˜10% Foetal Calf Serum (FCS) and ˜1% 200 mM L-Glutamine solution).

Plates were incubated overnight at 37° C. before addition of drug if cells were adherent. 200 μM of the test compound solutions (in 100% DMSO) were serially diluted across a 96 well plate. Each resulting point was then further diluted 1/10 into sterile distilled water (SDW).

To the cell negative blanks and compound negative control wells, 10% DMSO was added at 5% v/v. Assay plates were incubated for the following durations at 37° C. in 5% CO₂ in a humidified incubator for 72 hours. Following incubation, MIT solution to a final concentration of 1.5 μM was added to each well. The plates were then incubated for a further 4 hours at 37° C. in 5% CO₂ in a humidified incubator. The media was then removed, and the dye was solubilised in 200 μl DMSO (99.99%).

Plates were read at 540 nm absorbance using an Envision plate reader. Data was analysed using Microsoft Excel and GraphPad Prism and IC₅₀ values obtained.

Compound 11 has an IC₅₀ of 11.7 pM in this assay.

Renal Cell and AML Cell Lines Assays

The cytotoxicity of various free drug compounds was tested on a renal cell cancer cell line, 786-O, a Hodgkin lymphoma cell line, L428 and two AML cell lines, HL60 and HEL. For a 96-hour assay, cells cultured in log-phase growth were seeded for 24 h in 96-well plates containing 150 μL RPMI 1640 supplemented with 20% FBS. Serial dilutions of test article (i.e., free drug) in cell culture media were prepared at 4× working concentration; 50 μL of each dilution was added to the 96-well plates. Following addition of test article, the cells were incubated with test articles for 4 days at 37° C. Resazurin was then added to each well to achieve a 50 μM final concentration, and the plates were incubated for an additional 4 h at 37° C. The plates were then read for the extent of dye reduction on a Fusion HT plate reader (Packard instruments, Meridien, Conn., USA) with excitation and emission wavelengths of 530 and 590 nm, respectively. The IC₅₀ value, determined in triplicate, is defined here as the concentration that results in a 50% reduction in cell growth relative to untreated controls.

Referring to the following Table 1, the para-aniline compound 11 showed markedly increased activity on these cell lines as compared to the meta-aniline compound 19 in this assay.

TABLE 1 IC₅₀ Summary for Free Drugs [nM] Free Drug L428 786-O HL60 HEL Compound 11 <0.00001 <0.00001 <0.00001 <0.00001 Compound 19 1 0.5 0.6 0.2

Referring to the following Table 2, the activity of compounds 28, 30 and 32 is shown on L428, 786-O, HEL, HL-60 and MCF-7 cells, as well as the activity for compound 19 on MCF-7 cells.

TABLE 2 IC₅₀ Summary for Free Drugs [nM] Free Drug L428 786-O HEL HL-60 MCF-7 Compound <0.00001 <0.00001 <0.00001 <0.00001 <0.00001 28 Compound <0.00001 <0.00001 <0.00001 <0.00001 0.01 30 Compound <0.00001 <0.00001 <0.00001 <0.00001 1.0 32 Compound 5 19

Referring to the following Table 3, the activities of compounds 23, 25, are compared to that of compound 11 on 786-O, Caki-1, MCF-7, HL-60, THP-1, HEL, and TF1 cells. Cells were plated in 150 μL growth media per well into black-sided clear-bottom 96-well plates (Costar, Corning) and allowed to settle for 1 hour in the biological cabinet before placing in the incubator at 37° C., 5% CO₂. The following day, 4× concentration or drug stocks were prepared, and then titrated as 10-fold serial dilutions producing 8-point dose curves and added at 50 μl per well in duplicate. Cells were then incubated for 48 hours at 37° C., 5% CO₂. Cytotoxicity was measure by incubating with 100 μL Cell Titer Glo (Promega) solution for 1 hour, and then luminescence was measured on a Fusion HT plate reader (Perkin Elmer). Data was processed with Excel (Microsoft) and GraphPad (Prism) to produce dose response curves and IC50 values were generated and data collected.

TABLE 3 IC₅₀ Summary for Free Drugs [nM] Free Drug 786-O Caki-1 MCF-7 HL-60 THP-1 HEL TF1a Com- 0.4 0.2 1 0.01 1 0.03 1 pound 11 Com- 0.06 0.02 0.7 0.005 0.4 0.009 0.2 pound 23 Com- 0.09 0.06 0.8 0.01 0.9 0.02 0.9 pound25

In Examples 13 to 16, the following compounds are referred to by the compound numbers as show below:

Compound Alternative Designation 11 37 13 57 19 42 25 95 28 50 30 49 104 66

Example 13 Synthesis of PBD Drug Linker Compounds

General Information. In the following examples, all commercially available anhydrous solvents were used without further purification. Analytical thin layer chromatography was performed on silica gel 60 F254 aluminum sheets (EMD Chemicals, Gibbstown, N.J.). Radial chromatography was performed on Chromatotron apparatus (Harris Research, Palo Alto, Calif.). Analytical HPLC was performed on a Varian ProStar 210 solvent delivery system configured with a Varian ProStar 330 PDA detector. Samples were eluted over a C12 Phenomenex Synergi 2.0×150 mm, 4 μm, 80 Å reverse-phase column. The acidic mobile phase consisted of acetonitrile and water both containing either 0.05% trifluoroacetic acid or 0.1% formic acid (denoted for each compound). Compounds were eluted with a linear gradient of acidic acetonitrile from 5% at 1 min post injection, to 95% at 11 min, followed by isocratic 95% acetonitrile to 15 min (flow rate=1.0 mL/min). LC-MS was performed on a ZMD Micromass mass spectrometer interfaced to an HP Agilent 1100 HPLC instrument equipped with a C12 Phenomenex Synergi 2.0×150 mm, 4 μm, 80 Å reverse phase column. The acidic eluent consisted of a linear gradient of acetonitrile from 5% to 95% in 0.1% aqueous formic acid over 10 min, followed by isocratic 95% acetonitrile for 5 min (flow rate=0.4 mL/min). Preparative HPLC was carried out on a Varian ProStar 210 solvent delivery system configured with a Varian ProStar 330 PDA detector. Products were purified over a C12 Phenomenex Synergi 10.0×250 mm, 4 μm, 80 Å reverse phase column eluting with 0.1% formic acid in water (solvent A) and 0.1% formic acid in acetonitrile (solvent B). The purification method consisted of the following gradient of solvent A to solvent B: 90:10 from 0 to 5 min; 90:10 to 10:90 from 5 min to 80 min; followed by isocratic 10:90 for 5 min. The flow rate was 4.6 mL/min with monitoring at 254 nm. NMR spectral data were collected on a Varian Mercury 400 MHz spectrometer. Coupling constants (J) are reported in hertz.

(S)-2-((S)-2-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)-3-methylbutanamido)propandic add (36): To a solution of Val-Ala dipeptide 34 (200 mg, 1.06 mmol) dissolved in 10.6 mL anhydrous DMF was added maleimidocaproyl NHS ester 35 (327 mg, 1.06 mmol). Diisopropylethyamine (0.92 mL, 5.3 mmol) was then added and the reaction was stirred under nitrogen at an ambient temperature for 18 h, at which time TLC and analytical HPLC revealed consumption of the starting material. The reaction was diluted with 0.1 M HCl (100 mL), and the aqueous layer was extracted with ethyl acetate (100 mL, 3×). The combined organic layer was washed with water and brine, then dried over sodium sulfate, filtered and concentrated. The crude product was dissolved in minimal methylene chloride and purified by radial chromatography on a 2 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (95:5 to 90:10 CH₂Cl₂/MeOH) to provide 36 (158 mg, 39%) as an oily residue. TLC: R_(f)=0.26, 10% MeOH in CH₂Cl₂. ¹H NMR (CDCl₃) δ (ppm) 0.95 (d, J=17 Hz, 3H), 0.98 (d, J=17 Hz, 3H), 1.30 (m, 2H), 1.40 (d, J=17 Hz, 3H), 1.61 (m, 4H), 2.06 (m, 1H), 2.25 (dt, J=4.19 Hz, 2H), 3.35 (s, 1H), 3.49 (t, J=17 Hz, 2H), 4.20 (d, J=18 Hz, 1H), 4.38 (m, 1H), 6.80 (s, 2H). Analytical HPLC (0.1% formic acid): t_(R) 9.05 min. LC-MS: t_(R) 11.17 min, m/z (ES⁺) found 381.9 (M+H)⁺, m/z (ES⁻) found 379.9 (M−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((S)-1-(((S)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydra-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)hexanamide (38): A flame-dried 10 mL flask was charged with acid 36 (3.6 mg, 9.5 μmol), EEDQ (2.8 mg, 11.4 μmol), and 0.33 mL anhydrous CH₂Cl₂. Methanol (four drops, ˜80 μL) was added to facilitate dissolution and the mixture was stirred under nitrogen for 1 h. PBD dimer 37 (5.7 mg, 7.9 μmol) was then added and the reaction was stirred at room temperature for 6 h, at which time LC-MS revealed conversion to product. The reaction was concentrated, dissolved in minimal CH₂Cl₂, and purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 90:10 CH₂Cl₂/MeOH) to provide the drug linker 38 (3.9 mg, 45%). TLC: R_(f)=0.06, 5% MeOH in CH₂Cl₂. Analytical HPLC (0.1% formic acid): t_(R) 11.51 min. LC-MS: t_(R) 12.73 min, m/z (ES⁺) found 1089.6 (M+H)⁺, m/z (ES⁻) found 1087.3 (M−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-(4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)hexanamide (40): To a flame-dried 10 mL flask was added PBD dimer 37 (25 mg, 34.4 μmol), which was dissolved in 1.4 mL of a 10% MeOH in CHCl₃ solvent mixture. Maleimidocaproic acid (39) was added (7.3 mg, 34.4 μmol), followed by EEDQ (10.2 mg, 41.3 μmol) and pyridine (6 μL, 68.8 μmol). The reaction was stirred at room temperature under a nitrogen atmosphere for 14 h, at which time LC-MS revealed conversion to product. The reaction was concentrated, dissolved in minimal CH₂Cl₂, and purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 90:10 CH₂Cl₂/MeOH) to provide drug linker 40 (14.1 mg, 45%). LC-MS: t_(R) 12.81 min, m/z (ES⁺) found 918.9 (M+H)⁺, m/z (ES⁻) found 917.0 (M−H)⁻.

2-bromo-N-(4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)acetamide (41): To a flame-dried 10 mL flask was added PBD dimer 37 (16.5 mg, 22.7 μmol), which was dissolved in 0.9 mL of a 10% MeOH in CHCl₃ solvent mixture. Bromoacetic acid was added (3.2 mg, 22.7 μmol), followed by EEDQ (6.8 mg, 27.2 μmol). The reaction was stirred at room temperature under a nitrogen atmosphere for 4 h, at which time LC-MS revealed conversion to product. The reaction was concentrated, dissolved in minimal CH₂Cl₂, and purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 95:5 CH₂Cl₂/MeOH) to provide drug linker 41 (9.9 mg, 52%). TLC: R_(f)=0.09, 5% MeOH in CH₂Cl₂. LC-MS: t_(R) 12.44 min, m/z (ES⁺) found 848.1 (M+H)⁺, m/z (ES) found 845.7 (M−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((S)-1-(((S)-14(3-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)hexanamide (43): A flame-dried 10 mL flask was charged with acid 36 (3.6 mg, 9.4 μmol), EEDQ (2.8 mg, 11.3 μmol), and 0.38 mL anhydrous CH₂Cl₂ containing 1% methanol. The reaction was stirred under nitrogen for 1 h; PBD dimer 42 (6.8 mg, 9.4 μmol) was then added and the reaction was stirred at room temperature for 2 h, at which time LC-MS revealed conversion to product. The reaction was concentrated, dissolved in minimal CH₂Cl₂, and purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 90:10 CH₂Cl₂/MeOH) to provide drug linker 43 (3.1 mg, 30%), TLC: R_(f)=0.31, 10% MeOH in CH₂Cl₂, Analytical HPLC (0.1% formic acid): t_(R) 11.49 min. LC-MS: t_(R) 12.28 min, m/z (ES⁺) found 1089.5 (M+H)⁺, tn/z (ES⁻) found 1087.3 (M−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-(3-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)hexanamide (44): To a flame-dried 10 mL flask was added PBD dimer 42 (8.0 mg, 11 μmol), which was dissolved in 0.44 mL of a 10% MeOH in CH₂Cl₂ solvent mixture. Maleimidocaproic acid (39) was added (2.3 mg, 11 μmol), followed by EEDQ (3.3 mg. 13.2 μmol) and pyridine (1.8 μL, 22 μmol). The reaction was stirred at room temperature under a nitrogen atmosphere for 3 h, at which time LC-MS revealed conversion to product. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 90:10 CH₂Cl₂/MeOH) to provide drug linker compound 44 (1.2 mg, 12%). TLC: R_(f)=0.45, 10% MeOH in CH₂Cl₂. Analytical HPLC (0.05% trifluoroacetic acid): t_(R) 11.71 min. LC-MS: t_(R) 12.63 min, m/z (ES⁺) found 919.1 (M+H)⁺, m/z (ES⁻) found 917.1 (M−H)⁻.

(2S,3R,4S,5R,6R)-2-(2-(3-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)propanamido)-4-((((3-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)carbamoyl)oxy)methyl)phenoxy)-6-methyltetrahydro-2H-pyran-3,4,5-triyl triacetate (46): A flame-dried flask was charged with glucuronide linker intermediate 45 (reference: Jeffrey et al., Biaconjugate Chemistry, 2006, 17, 831-840) (15 mg, 20 μmol), 1.4 mL anhydrous CH₂Cl₂, pyridine (20 μL, 240 μmol), and then cooled to −78° C. under nitrogen. Diphosgene (3.0 μL, 24 old) was then added and the reaction was stirred for 2 h at −78° C., after which time a small aliquot was quenched with methanol and analyzed by LC-MS for formation of the methyl carbonate, which confirmed formation of the glucuronide chloroformate. PBD dimer 42 (15 mg, 20 μmol) was then dissolved in 0.7 mL anhydrous CH₂Cl₂ and added dropwise to the reaction vessel. The reaction was warmed to 0° C. over 2 h and then diluted with 50 mL CH₂Cl₂.

The organic layer was washed with water (50 mL), brine (50 mL), dried over sodium sulfate, filtered and concentrated. The crude reaction product was purified by radial chromatography on a 1 mm chromatotron plate eluted 10% MeOH in CH₂Cl₂ to provide 46 (5.7 mg, 19%). TLC: R_(f)=0.47, 10% MeOH in CH₂Cl₂. Analytical HPLC (0.1% formic acid): t_(R) 12.09 min. LC-MS: t_(R) 14.05 min, miz (ES⁺) found 1500.3 (M+H)⁺.

(2S,3S,4S,5R,6S)-6-(2-(3-aminopropanamido)-4-((((3-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11 a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)carbamoyl)oxy)methyl)phenoxy)-3,4,5-trihydroxytetrahydro-2H-pyran-2-carboxylic acid (47): A flask containing 46 (5.7 mg, 3.8 μmol) dissolved in a solvent mixture of 0.2 mL each of MeOH, tetrahydrofuran, and water was cooled to 0° C. To the stirred solution was added lithium hydroxide monohydrate (0.8 mg, 19 μmol) and the reaction was stirred at room temperature for 4 h, at which time LC-MS indicated conversion to product. Glacial acetic acid (1.1 μL, 19 μmol) was added and the reaction was concentrated to provide 47, which was carried forward without further purification. LC-MS: t_(R) 11.59 min, m/z (ES⁺) found 1138.4 (M+H)⁺.

(2S,3S,4S,5R6S)-6-(2-(3-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)propanamido)-4-((((3-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)carbamoyl)oxy)methyl)phenoxy)-3,4,5-trihydroxytetrahydro-2H-pyran-2-carboxylic acid (48): To a solution of 47 (4.3 mg, 3.8 umol) dissolved in 0.38 mL anhydrous DMF was added maleimidocaproyl NHS ester 35 (1.2 mg, 3.8 umol), followed by diisopropylethylamine (4.0 uL, 22.8 umol). The reaction was stirred at room temperature under nitrogen for 2 h, at which time LC-MS revealed conversion to product. The reaction was diluted with a mixture of acetonitrile (0.5 mL), DMSO (1 mL), water (0.5 mL), and then purified by preparative HPLC. The mobile phase consisted of A=water and B=acetonitrile, both containing 0.1% formic acid. A linear elution gradient of 90:10 A:B to 10:90 A:B over 75 minutes was employed and fractions containing the desired product were lyophilized to provide drug linker compound 48 (1.2 mg, 24% over two steps). Analytical HPLC (0.1% formic acid): t_(R) 10.85 min. LC-MS: t_(R) 12.12 min, m/z (ES⁺) found 1331.4 (M+H)⁺, m/z (ES⁻) found 1329.5 (M−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((S)-1-(((S)-1-((3-((S)-7-methoxy-8-((5-(((S)-7-methoxy-2-(4-(4-methylpiperazin-1-yl)phenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)pentyl)oxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)hexanamide (51): A flame-dried 10 mL flask was charged with acid 36 (2.7 mg, 7.1 μmol), EEDQ (2.1 mg, 8.5 μmol), and 0.28 mL anhydrous CH₂Cl₂containing 1% methanol. The reaction was stirred under nitrogen for 1 h; PBD dimer 49 (5.8 mg, 7.1 μmol) was then added and the reaction was stirred at room temperature for 20 h, at which time LC-MS revealed conversion to product. The reaction was concentrated then purified by preparative HPLC and fractions containing the desired product were lyophilized to provide drug linker compound 51 (2.7 mg, 32%). Analytical HPLC (0.1% formic acid): t_(R) 9.17 min, LC-MS: t_(R) 11.25 min, m/z (ES⁺) found 1185.3 (M+H)⁺, m/z (ES⁻) found 1182.9 (M−H)⁻.

N-((S)-1-(((S)-1-((3-((S)-8-((5-(((S)-2-(4-(3-(dimethylamino)propoxy)phenyl)-7-methoxy-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)pentyl)oxy)-7-methoxy-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)-6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamide (52): A flame-dried 10 mL flask was charged with acid 36 (3.7 mg, 9.7 μmol), EEDQ (2.9 mg, 11.6 μmol), and 0.4 mL anhydrous CH₂Cl₂ containing 1% methanol. The reaction was stirred under nitrogen for 1 h; PBD dimer 50 (8.0 mg, 9.7 μmol) was then added and the reaction was stirred at room temperature for 6 h, at which time LC-MS revealed the presence of product. The reaction was concentrated then purified by preparative HPLC and fractions containing the desired product were lyophilized to provide drug linker compound 52 (3.1 mg, 25%), Analytical HPLC (0.1% formic acid): t_(R) 9.45 min. LC-MS: t_(R) 11.75 min, m/z (ES⁺) found 1188.4 (M+H)⁺, m/z (ES⁻) found 1186.0 (M−H)⁻.

4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((S)-1-(((S)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-11H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)benzamide (54): To a flame-dried 10 mL flask was added linker fragment 53 (7.7 mg, 20 μmol), which was dissolved in 0.33 mL of a 5% MeOH in CH₂Cl₂ solvent mixture. EEDQ (6.1 mg, 25 μmol) was added and the reaction was stirred at room temperature under nitrogen for 15 minutes, at which time PBD dimer 37 (12 mg, 16.5 μmol) was added. The reaction was stirred at room temperature under a nitrogen atmosphere for an additional 3 h, at which time LC-MS revealed conversion to product. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 90:10 CH2Cl₂/MeOH) to provide 54 (2.4 mg, 13%). TLC: R_(f)=0.44, 10% MeOH in CH₂Cl₂. Analytical HPLC (0.05% trifluoroacetic acid): t_(R) 11.53 min, LC-MS: t_(R) 12.61 min, m/z (ES⁺) found 1095.4 (M+H)⁺, m/z (ES) found 1093.9 (M−H)⁻.

(S)-2-(2-iodoacetamido)-N-((S)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)-3-methylbutanamide (56): A flame-dried flask was charged with linker 55 (7.8 mg, 22 μmol), which was dissolved in 0.37 mL of a 5% MeOH in CH₂Cl₂ solvent mixture. EEDQ (6.8 mg, 27.5 μmol) was added and the reaction was stirred at room temperature under nitrogen for 15 minutes, at which time PBD dimer 37 (13 mg, 18 μmol) was added. The reaction was stirred at room temperature under a nitrogen atmosphere for an additional 4 h, at which time LC-MS revealed conversion to product. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 80:20 CH₂Cl₂/MeOH) to provide 56 (3.5 mg, 18%). Analytical HPLC (0.1% formic acid): t_(R) 11.43 min. LC-MS: t_(R) 12.49 min, m/z (ES⁺) found 1064.6 (M+H)⁺, m/z (ES⁻) found 1098.9 (M+2H₂O−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((S)-1-(((S)-1-((4-((S)-7-methoxy-8-((5-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-11-1-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)pentyl)oxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)hexanamide (58): To a flame-dried 10 mL flask was added linker fragment 36 (19 mg, 50 μmol), which was dissolved in 0.33 mL of a 5% MeOH in CH₂Cl₂ solvent mixture. EEDQ (12.4 mg, 50 μmol) was added and the reaction was stirred at room temperature under nitrogen for 15 minutes, at which time PBD dimer 57 (12.5 mg, 16.6 μmol) was added. The reaction was stirred at room temperature under a nitrogen atmosphere for an additional 5 h, at which time LC-MS revealed conversion to product. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 80:20 CH₂Cl₂/MeOH) to provide 58 (2.1 mg, 11%). Analytical HPLC (0.1% formic acid): t_(R) 12.19 min. LC-MS: t_(R) 12.58 min, m/z (ES⁺) found 1117.8 (M+H)⁺, m/z (ES⁻) found 1133.7 (M+H₂O−H)⁻.

(R)-2-((R)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-methylbutanamido)propanoic acid (60): A flame dried flask was charged with Fmoc-D-Valine (200 mg, 0.59 mmol) and 5.9 mL anhydrous THF. N-hydroxysuccinimide (75 mg, 0.65 mmol) was added, followed by diisopropylcarbodiimide (0.1 mL, 0.65 mmol), and the reaction was stirred at an ambient temperature overnight, at which time LC-MS revealed conversion to product. The reaction mixture was diluted with CH₂Cl₂ and washed with water (50 mL), brine (50 mL), dried over sodium sulfate and concentrated to dryness. The material was carried forward without further purification. LC-MS: t_(R) 13.89 min, m/z (ES⁺) found 437.0 (M+H)⁺. Crude Fmoc-D-Val-OSu (0.59 mmol) was dissolved in dimethoxyethane (1.5 mL) and THF (0.8 mL). D-alanine (73 mg, 0.89 mmol) was dissolved in 2.3 mL water and added to the reaction mixture, followed by sodium bicarbonate (99 mg, 1.2 mmol). The resulting slurry was stirred at room temperature overnight, at which time the reaction had clarified and LC-MS revealed completion. The reaction was poured into 50 mL CH₂Cl₂ and the organic layer was washed with 50 mL 0.1 M HCl and then brine, dried over sodium sulfate, and then concentrated to dryness. The crude product was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂ to provide 60 (128 mg, 54%). TLC: R_(f)=0.18, 10% MeOH in CH₂Cl₂. Analytical HPLC (0.1% formic acid): t_(R) 9.47 min. LC-MS: t_(R) 13.09 min, m/z (ES⁺) found 411.1 (M+H)⁺, m/z (ES⁻) found 409.2 (M−H)⁻.

(R)-2-((R)-2-(6-(2,5-dioxa-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)-3-methylbutanamido)propanoic add (61): Protected dipeptide 60 (70 mg, 0.37 mmol) was suspended in 6 mL anhydrous CH₂Cl₂, cooled on ice under nitrogen, and 2 mL of diethylamine was added dropwise. The reaction was warmed to room temperature and stirred under nitrogen for 2 h, at which time HPLC revealed consumption of starting material. The reaction was diluted with 6 mL of chloroform and concentrated. The crude reaction residue was re-dissolved in 6 mL chloroform and concentrated twice, followed by drying on a vacuum line for 2 h. The deprotected dipeptide was then dissolved in 3.7 mL anhydrous DMF. MC-OSu (138 mg, 0.44 mmol) was then added, followed by diisopropylethylamine (0.32 mL, 1.9 mmol). The reaction was stirred under a nitrogen atmosphere at room temperature overnight. Workup was achieved by pouring the reaction in to 50 mL 0.1 M HCl and extracting with ethyl acetate (50 mL, 3×). The combined organic layer was washed with water (50 mL) and brine (50 mL), dried over sodium sulfate, and concentrated. The crude product was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (99:1 to 95:5 CH₂Cl₂/MeOH) to provide 61 (14 mg, 22%). ¹H NMR (CD₃OD) δ (ppm) 0.94 (d, J=14 Hz, 3H), 0.98 (d, J=14 Hz, 3H), 1.29 (m, 2H), 1.39 (d, J=7.4 Hz, 3H), 1.61 (m, 4H), 2.05 (m, 1H), 2.25 (dt, J=1.2, 7.4 Hz, 2H), 3.48 (t, J=7 Hz, 2H), 4.19 (m, 1H), 4.37 (m, 1H), 6.78 (s, 2H). Analytical HPLC (0.1% formic acid): t_(R) 10.04 min. LC-MS: t_(R) 11.22 min, m/z (ES⁺) found 382.1 (M+H)⁺, m/z (ES⁻) found 380.0 (M−H)⁻.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((R)-1-(((R)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)hexanamide (62): To a flame-dried 10 mL flask was added linker 61 (9.5 mg, 25 μmol), which was dissolved in 0.33 mL of a 5% MeOH in CH₂Cl₂ solvent mixture. EEDQ (7.3 mg, 30 μmol) was added and the reaction was stirred at room temperature under nitrogen for 15 minutes, at which time PBD dimer 37 (12 mg, 16.5 μmol) was added. The reaction was stirred at room temperature under a nitrogen atmosphere for an additional 3 h, at which time LC-MS revealed conversion to product. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 80:20 CH₂Cl₂/MeOH) to provide 62 (2.8 mg, 16%). TLC: R_(f)=0.39, 10% MeOH in CH₂Cl₂. Analytical HPLC (0.1% formic acid): t_(R) 11.50 min. LC-MS: t_(R) 12.50 min, m/z (ES⁺) found 1089.7 (M+H)⁺, m/z (ES⁻) found 1088.0 (M−H)⁻.

(S)-2-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)propanoic acid (64): L-alanine (58 mg, 0.65 mmol) was suspended in 6.5 mL anhydrous DMF and MC-OSu 35 (100 mg, 0.324 mmol) was then added. Diisopropylethylamine (0.28 mL, 1.6 mmol) was added and the reaction was stirred overnight at room temperature under nitrogen. The reaction was then diluted with 50 mL 0.1 M HCl and the aqueous layer was then extracted with ethyl acetate (50 mL, 3×). The combined organic layer was then washed with water (50 mL) and brine (50 mL), dried over sodium sulfate, and then concentrated to dryness. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (97.5:2.5 to 90:10 CH₂Cl₂/MeOH) to provide 64 (25 mg, 27%). TLC: R_(f)=0.25, 10% MeOH in CH₂Cl₂. ¹H NMR (CD₃OD) δ (ppm) 1.30 (m, 2H), 1.37 (d, J=7.4 Hz, 3H), 1.60 (m, 4H), 2.21 (t, J=7.4 Hz, 2H), 3.48 (t, J=7 Hz, 2H), 4.35 (q, J=7.4 Hz, 1H), 6.78 (s, 2H). Analytical HPLC (0.1% formic acid): tp, 9.06 min.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-((S)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)hexanamide (65): To a flame-dried 10 mL flask was added linker 64 (14 mg, 50 μmol), which was dissolved in 0.66 mL of a 5% MeOH in CH₂Cl₂ solvent mixture. EEDQ (15 mg, 60 μmol) was added and the reaction was stirred at room temperature under nitrogen for 15 minutes, at which time PBD dimer 37 (24 mg, 33 μmol) was added. The reaction was stirred at room temperature under a nitrogen atmosphere for an additional 4 h. The reaction was purified by radial chromatography on a 1 mm chromatotron plate eluted with CH₂Cl₂/MeOH mixtures (100:0 to 90:10 CH₂Cl₂/MeOH) to provide 65 (3.5 mg, 11%). Analytical HPLC (0.1% formic acid): t_(R) 11.40 min. LC-MS: t_(R) 12.39 min, m/z (ES⁺) found 990.6 (M+H)⁺, m/z (ES⁻) found 989.0 (M−H)⁻.

PBD dimer 57 linked directly through maleimidocaproyl spacer (Scheme 14): PSC) dimer 57 is coupled to maleimidocaproic acid 39 employing the chemistry described in Scheme 2.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-(2-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)hexanamide (68): To a mixture of the 66 (10 mg, 0.013 mmol) in CH₂Cl₂ (300 μL) was added DIPEA and MC-Cl (67) (3 mg, 0.013 mmol). After 1h, an additional 3 equiv. of DIPEA (7 μL) and 2 equiv. of the acid chloride (6 mg, 0.026 mmol) were added. After 1 h, an additional quantity of DIPEA (7 μL) and acid chloride (6 mg, 0.026 mmol) were added. After an additional 3 h, the reaction mixture was aspirated directly onto a 1 mm radial chromatotron plate and eluted with dichloromethane followed by a gradient of methanol (1% to 5%) in dichloromethane. Product containing fractions, as a mixture with the starting aniline, were concentrated to a residue and dissolved in a mixture of 0.5 mL DMSO, 0.5 mL acetonitrile and 0.5 mL deionized water and was further purified by preparative HPLC. The major peak was collected and the fractions were combined, frozen and lyophilized to give 2.1 mg (18%): MS (ES⁺) m/z 919.2 [M+H]⁺.

Note: Acid chloride 67 was prepared by dissolving 100 mg of 39 in oxalyl chloride (5 mL). A drop of DMF was added and the mixture was stirred at an ambient temperature for several hours before being concentrated under reduced pressure. Dichloromethane was added and the mixture was concentrated a second time to afford an off-white solid which was used directly: ¹H-NMR (400 MHz, CDCl₃) δ 6.70 (s, 2H), 3.46 (t, J=7 Hz, 2H), 2.82 (t, J=7.2 Hz, 2H), 1.72 (pent, J=7.6 Hz, 2H), 1.61 (pent, J=7.4 Hz, 2H), 1.35 (pent, J=7.6 Hz, 2H).

tert-butyl 2-(2-aminoacetamido)acetate (69): To a mixture of the glycine tert-butyl ester hydrogen chloride salt (70) (484 mg, 2.9 mmol) in dichloromethane (25 mL) was added Fmoc-Gly-OH (71) (0.861 mg, 2.99 mmol), DIPEA (756 mg, 4.35 mmol) and HATU (1.3 g, 3.5 mmol). The reaction mixture was stirred at an ambient temperature for 16 h and then poured into ethyl acetate and was washed with water (3×) and brine (1×). The organic phase was dried over MgSO4, filtered and concentrated under reduced pressure. The resulting residue was purified via radial chromatography on a 2 mm plate eluting with 5% methanol/dichloromethane. Product containing fractions were concentrated under reduced pressure and treated with 20% piperidine/dichloromethane (10 mL) for 1 h, before being concentrated under reduced pressure and then purified twice via radial chromatography on a 2 mm plate eluting with a gradient of 5 to 10% methanol/dichloromethane to provide (200 mg, 37%): ¹H-NMR (400 MHz, CDCl₃) 7.62 (s, 1H), 4.00 (s, 2H), 3.39 (s, 2H), 1.47 (s, 9H).

2-(2-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)acetamido)acetic acid (72): To a solution of the amine 69 (200 mg, 0.11 mmol) in DMF (1 mL) was added 35 (350 mg, 0.11 mmol) and the reaction mixture was allowed to stir at an ambient temperature for 2 h. The mixture was concentrated under reduced pressure and was purify by radial chromatography on a 1 mm plate eluting with dichloromethane and a gradient of methanol (1 to 5%) in dichloromethane. Product containing fractions were concentrated under reduced pressure, dissolved in dichloromethane (4 mL) and treated with trifluoroacetic acid (4 mL). After 40 min the mixture was concentrated under reduced pressure and the resulting residue was dissolved in dichloromethane and concentrated to give 22.5 mg (19%) of 72 as white solid: ¹H-NMR (400 MHz, CD₃OD) δ 6.79 (s, 2H), 3.93 (s, 2H), 3.89 (s, 2H), 3.49 (t, J=6.8 Hz, 2H), 2.26 (t, J=6.8 Hz, 2H), 1.61 (m, 4H), 1.34 (m, 2H); MS (ES⁺) m/z 326.21 [M+H]⁺.

6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N-(2-((2-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzediazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-2-oxoethyl)amino)-2-oxoethyl)hexanamide (73): To a mixture of 72 (15 mg, 0.046 mmol) in 5% methanol/dichloromethane (0.5 mL) was added EEDQ (11 mg, 0.046 mmol) and the mixture was stirred for 30 min at an ambient temperature, at which time 37 (16 mg, 0.023 mmol) was added. The reaction mixture was stirred for 3 h and was purified directly on a 1 mm radial chromatotron plate eluting with a 1% to 4% methanol/dichloromethane gradient to give 6.8 mg (29%) of 73 as a yellow solid: MS (ES⁺) m/z 1033.57 [M+H]⁺.

(S)-tert-butyl 1-((S)-pyrrolidine-2-carbonyl)pyrrolidine-2-carboxylate (74): To a mixture of L-proline-tert-butyl ester hydrogen chloride salt 75 (0.5 g, 2.9 mmol) in dichloromethane (50 mL) was added 76 (0.98 g, 2.99 mmol), DIPEA (756 mg, 4.35 mmol) and HATU (1.3 g, 3.5 mmol). The reaction mixture was allowed to stir at an ambient temperature for 16 h. The mixture was poured into ethyl acetate (100 mL) and was washed with 0.2 N HCl (50 mL), water (50 mL), brine (50 mL) and dried over MgSO₄. Chromatography was conducted on a 2 mm radial chromatotron plate eluting with 10% ethyl acetate in hexanes. Product-containing fractions were concentrated under reduced pressure, dissolved in dichloromethane (8 mL) and treated with piperidine (2 mL). The mixture was stirred for 1 h, concentrated under reduced pressure and purified on a 2 mm radial chromatotron plate eluting with 5% methanol/dichloromethane. This gave 200 mg (26%) of the dipeptide 74: ¹H-NMR (400 MHz, CDCl₃) δ 4.41 (m, 1H), 4.17 (m, 1H), 3.82 (m, 1H), 3.57 (m, 4H), 3.2 (m, 1H), 2.82 (m, 1H), 2.83-1.65 (m, 5H), 1.44 (m, 9H).

(S)-tert-butyl 1-((S)-1-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoyl)pyrrolidine-2-carbonyl)pyrrolidine-2-carboxylate (77): To a mixture of the amine 74 (200 mg, 0.75 mmol), 39 (190 mg, 0.9 mmol) and DIPEA (032 mL, 1.8 mmol) was added HATU (342 mg, 0.9 mmol) and the mixture was allowed to stir at an ambient temperature for 5 h. The mixture was poured into ethyl acetate (100 mL) and washed with water (3×100 mL) and brine (1×100 mL). The organic phase was dried over magnesium sulfate, filtered and concentrated. The resulting residue was subjected to radial chromatography on a 2 mm radial chromatotron plate eluting with dichloromethane followed by an increasing gradient of 1 to 5% methanol in dichloromethane. Two additional purifications, both eluting with a gradient of 1 to 5% methanol in dichloromethane, first on a 2 mm plate and then on a 1 mm plate afforded 113 mg (33%) of 77 as an white solid: ¹H-NMR (400 MHz, CDCl₃) δ 4.63 (m, 1H), 4.41 (m, 1H), 3.82 (m, 1H), 3.6 3 (m, 1H), 3.55 (m, 1H), 3.45 (m, 3H), 2.38-1.83 (m, 10H), 1.70-1.50 (m, 5H), 1.45 (m, 9H), 1.35 (m, 2H); MS (ES⁺) m/z 462.33 [M+H]⁺.

(S)-1-((S)-1-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoyl)pyrrolidine-2-carbonyl)pyrrolidine-2-carboxylic acid (78): To a mixture of the tert-butyl ester 77 in dichloromethane (4 mL) was added trifluoroacetic acid (4 mL). After 40 min the reaction was determined to be complete by HPLC analysis. The mixture was concentrated under reduced pressure and the resulting residue was dissolved in dichloromethane and concentrated a second time to give 37 mg (100%) of 78 as a white solid: ¹H-NMR (400 MHz, CDCl₃) δ 6.68 (s, 2H), 4.62 (m, 2H), 3.81 (m, 1H), 3.70 (m, 1H), 3.57 (m, 2H), 3.45 (m, 2H), 2.40-1.91 (m, 10H), 1.70-1.45 (m, 4H), 1.33 (m, 2H); MS (ES⁺) m/z 406.2 [M+H]⁺.

1-(1-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoyl)pyrrolidine-2-carbonyl)-N-(4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)pyrrolidine-2-carboxamide (79): To a mixture of the 78 (9.3 mg, 0.023 mmol) in 5% methanol/dichloromethane (0.4 mL) was added EEDQ (7 mg, 0.027 mmol). The mixture was stirred for 15 min at an ambient temperature and then 37 (15 mg, 0.021 mmol) was added. The mixture was stirred for 4 h, the reaction mixture was diluted with dichloromethane (2mL) and was aspirated directly onto a 1 mm radial chromatotron plate. The product was eluted with a gradient of 1 to 5% methanol in dichloromethane to provide 6.8 mg (29%) of 79 as a yellow solid: MS (ES⁺) m/z 1113.51 [M+H]⁺.

(S)-5-(allyloxy)-2-((S)-2-(((allyloxy)carbonyl)amino)-3-methylbutanamido)-5-oxopentanoic acid (80): To a mixture of the 2-chlorotrityl resin (1.0 g, 1.01 mmol) suspended in dichloromethane (10 ml) was added Fmoc-Glu-(OAllyl)-OH (81) (409 mg, 1.0 mmol) and DIPEA (173 μL, 1.0 mmol). The reaction mixture was shaken for 5 min, and an additional portion of DIPEA (260 μL, 1.5 mmol) was added and the mixture was shaken for 1 h. Methanol (0.8 mL) was added and the mixture was shaken for 5 min, before being filtered and washed with DMF (6×), dichloromethane (6×), diethyl ether (6×) and dried under reduced pressure. The resulting resin was subjected to 20% piperidine in dichloromethane (10 mL) for 1 h, before being filtered and washed with DMF (6×), dichloromethane (6×), diethyl ether (6×) and dried under reduced pressure.

To a mixture of the Fmoc-Val-OH (82) (1.03 g, 3.30 mmol)) in DMF (7 mL) was added DIPEA (1.0 mL) and HATU (1.1 g, 3.03 mmol). After thorough mixing, the solution as aspirated into a 10 mL syringe containing the resin prepared above. The mixture was capped and shaken for 16 h. The resin was washed with DMF (6×), dichloromethane (6×) and ether (6×). A small portion (10 mg) was isolated and treated with 20% TFA/Dichloromethane and the resulting solution analyzed by LC-MS which revealed one high purity peak which displayed the correct mass (MS (ES⁺) m/z 509.28 [M+H]⁺). The remaining resin was then treated with 20% piperidine/DMF (8 mL) for 2 h, before being washed with DMF (6×), dichloromethane (6×), diethyl ether (6×) and dried under reduced pressure.

A mixture of allyl chloroformate (529 μL, 5.05 mmol), DIPEA (1.7 mL, 10 mmol) in dichloromethane (10 mL) was prepared and aspirated into a syringe containing the resin above. The mixture was capped and shaken. After approximately 2 h, the reaction mixture was drained, and washed with dichloromethane (6×). A small portion of the resin (˜10 mg) was cleaved with 20% TFA/dichloromethane and analyzed by LC-MS for masses of starting material and product. The main component was still the unreacted amine, so the resin was again subjected to the conditions described above. After 4 h, the resin was washed with dichloromethane (6×), and then treated repeatedly with 5% TFA in dichloromethane (4×7 mL). The resulting solution was concentrated under reduced pressure. The mixture was purified on a 2 mm radial chromatotron plate eluting with 5% methanol/dichloromethane to give 107 mg of 80: ¹H-NMR (400 MHz, CDCl₃) δ 7.05 (s, 1H), 5.90 (m, 2H), 5.57 (d, 1H), 5.29 (d, J=14.7 Hz, 2H), 5.22 (t, J=10.9 Hz, 2H), 4.59 (m, 5H), 4.02 (m, 1H), 2.60-2.40 (m, 2H), 2.37-2.18 (m, 1H), 2.17-2.02 (m, 2H), 0.96 (d, J=6.4 Hz, 3H), 0.93 (d, J=6.6 Hz, 3H); MS (ES⁺) m/z 371.12 [M+H]⁺.

(S)-allyl 4-((S)-2-(((allyloxy)carbonyl)amino)-3-methylbutanamido)-5-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-5-oxopentanoate (83): To a mixture of the acid 80 (30, 0.04 mmol) in 5% methanol/dichloromethane (1 mL) was added EEDQ (20 mg, 0.082 mmol). The mixture was stirred for 30 min at an ambient temperature and then 37 (30 mg, 0.04 mmol) was added and the mixture was stirred for approximately 5 h. Partially purification by aspirating directly onto a 1 mm radial chromatotron plate and eluting with a gradient of 1% to 5% methanol/dichloromethane afforded a mixture of desired product and 37 (26 mg; ˜3:1 respectively) which was carried forward without further purification.

(S)-4-((S)-2-amino-3-methylbutanamido)-5-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-5-oxopentanoic add (84): To the mixture of 83 and 37 (26 mg) in anhydrous dichloromethane (3 mL) was added Ph₃P (0.3 mg, 0.0012 mmol), pyrrolidine (4 μL, 0.048 mmol) and tetrakis palladium (0.7 mg, 0.6 μmol). After 2 h, an additional quantity (0.7 mg, 0.6 μmol) of tetrakis palladium was added and the reaction was allowed to stir for an additional 1 hr before being concentrated under reduced pressure. The residue was dissolved in DMSO (1 mL), acetonitrile with 0.05% formic acid (1 mL) and water with 0.05% formic acid (1 mL) and purified by preparative reverse phase HPLC. A single fraction of product was collected and lyophilized to give 6 mg (14% for two steps) of 84: MS (ES⁺) m/z 1078.6 [M+H]⁺.

(S)-4-((S)-2-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)-3-methylbutanamido)-5-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazapin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-5-oxopentande add (85): To a mixture of the 84 (6 mg, 6 μmol), and 35 (2 mg, 6 μmol) in DMF (200 μL) was added DIPEA (3 μL, 18 μmol) and the reaction mixture was stirred at an ambient temperature. After 1 h, an additional equivalent of 35 (2 mg, 6 μmol) was added and the reaction was allowed to continue to stir at an ambient temperature for 3 h. A third equivalent of 35 (2 mg, 6 μmol) was added and the mixture was stirred for approximately 1 h, concentrated under reduced pressure, dissolved in dichloromethane and aspirated directly onto a 1 mm radial chromatotron plate and eluted with 5% methanol in dichloromethane. This gave 2.5 mg (36%) of high purity 85: MS (ES⁺) m/z 1147.49 [M+H]⁺.

(21S,24S)-1-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-21-isopropyl-24-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)carbamoyl)-3,19,22-trioxo-7,10,13,16-tetraoxa-4,20,23-triazaheptacosan-27-oic add (86): To a mixture of the 84 (8 mg, 8.4 μmol) and Mal-PEG4-NHS (87) (6.5 mg, 12.6 μmol) in DMF (200 μL) was added DIPEA (4.3 μL, 25 μmol). The reaction mixture was stirred at an ambient temperature for 2 h, and was concentrated under reduced pressure. The resulting residue was dissolved in dichloromethane and aspirated onto a 1 mm radial chromatotron plate. The material was polar and did not chromatograph on the silica gel-based chromatotron plate. The plate was eluted with methanol to recover the mixture which was isolated under reduced pressure. The residual material was purified via preparative reverse phase HPLC. A single main peak eluted and the fractions were combined, frozen and lyophilized to a residue of 0.9 mg (8%) of 86: MS (ES⁺) m/z 1353.04 [M+H]⁺.

(S)-6-(dimethylamino)-2-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)hexanoic acid (88): To a mixture of the 2-chlorotrityl resin (1 g, 1.01 mmol) in CH₂Cl₂ (10 ml) was added Fmoc-Lys(Me)2-OH (89) (432 mg, 1.0 mmol) and DIPEA (433 μL, 2.5 mmol). The reaction mixture was shaken for 1 h. Methanol (0.8 mL) was added and the mixture was shaken for an additional 5 min, before being filtered and washed with DMF (6×), dichloromethane (6×), diethyl ether (6×) and dried under reduced pressure. The dried resin was subjected to 20% piperidine in DMF (10 mL) for 1 h, before being filtered and washed with DMF (6×), dichloromethane (6×), diethyl ether (6×).

To a mixture of the 39 (3.0 mmol, 633 mg) in DMF (7 mL) was added DIPEA (1.0 mL) and HATU (1.1 g, 3.03 mmol). After thorough mixing, the solution as aspirated into a 10 mL syringe containing the resin above. The mixture was capped, shaken for 16 h, filtered and the resin washed with DMF (6×), dichloromethane (6×), and ethyl ether (6×). The resin was by repeatedly treating with 5% TFA/dichloromethane (6 mL×5), shaking for 1 min, and then filtering. The resulting solution was concentrated under reduced pressure and under high vacuum. The material was purified by preparatory reverse phase HPLC to give 208 mg of 88: ¹H-NMR (400 MHz, CD₃OH/CDCl₃ 1:1 mixture) δ 6.73 (s, 2H), 4.41 (m, 1H), 3.48 (t, 2H), 3.31 (s, 1H), 3.03 (m, 2H), 2.84 (s, 6H), 2.22 (m, 2H), 1.87 (m, 2H), 1.78-1.52 (m, 6H), 1.43 (m, 2H), 1.31 (pent, 2H); MS (ES⁺) m/z 386.28 [M+H]⁺.

(S)-6-(dimethylamino)-2-(6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanamido)-N-(4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11 a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11 a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)hexanamide (90): To a mixture of the 88 (9.3 mg, 0.023 mmol) in 5% methanol/dichloromethane (400 μL) was added EEDQ (7 mg, 0.027 mmol). The mixture was stirred for 30 min at an ambient temperature and then 37 (15 mg, 0.021 mmol) was added. After 4 h, the mixture was concentrated under reduced pressure, dissolved in a mixture of DMSO (1 mL), acetonitrile (2 mL containing 0.05% formic acid) and water (1 mL containing 0.05% formic acid) and purified by reverse-phase HPLC (method A). Product containing fractions were contaminated with 37, so the fractions were lyophilized to a residue and repurified as described above to give 0.5 mg (2%) of pure 90: MS (ES⁺) m/z 537.46 [M+H]/2⁺.

Allyl ((S)-1-(((S)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)carbamate (91): To a mixture of the 92 (45 mg, 0.123 mmol) in 5% methanol/dichloromethane (1 mL) was added EEDQ (30.4 mg, 0.123 mmol). The mixture was stirred for 30 min at an ambient temperature and then 37 (30 mg, 0.041 mmol) was added. The reaction mixture was stirred for approximately 5 h and then purified on a 1 mm radial chromatotron plate eluting with 5% methanol/dichloromethane to give 22 mg (55%) of 91 which was not characterized but carried on directly.

1-(3-(2,5-dioxo-2.5-dihydro-1H-pyrrol-1-yl)propanamido)-N-((S)-1-(((S)-1-((4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)propoxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)phenyl)amino)-1-oxopropan-2-yl)amino)-3-methyl-1-oxobutan-2-yl)-3,6,9,12-tetraoxapentadecan-15-amide (93): To a solution of the 91 (22 mg, 0.022 mmol) in anhydrous dichloromethane (3 mL) was added Ph₃P (0.3 mg, 0.0012 mmol), pyrrolidine (4 μL, 0.048 mmol) and tetrakis palladium (0.7 mg, 6 μmol). After approximately 2 h, the reaction mixture was purified on a 1 mm radial chromatotron plate eluting with 5% to 10% methanol/dichloromethane. The major band was collected and concentrated to a residue which was dissolved in DMF (0.2 mL) and reacted with NHS ester 87 (10 mg, 0.19 mmol). The reaction was allowed to stir for 30 min, concentrated and purified by radial chromatography on a 1 mm plate eluting with 5% methanol/dichloromethane to give 3.2 mg (11%) of 93: MS (ES⁺) m/z 1294.7 [M+H]⁺.

(E)-6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-N′-(4-((S)-7-methoxy-8-((5-(((S)-7-methoxy-2-(4-methoxyphenyl)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yl)oxy)pentyl)oxy)-5-oxo-5,11a-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-2-yl)benzylidene)hexanehydrazide (94): To a mixture of the aldehyde 95 (5.4 mg, 7 μmol) in 5% methanol/dichloromethane at 0° C. was added the hydrazide-TFA salt 96 (4.5 mg, 14 μmol). The reaction mixture was allowed to warm to an ambient temperature and stir for 5 h before being concentrated under reduced pressure and purified on a silica gel column eluting with 3% methanol/dichloromethane to give 2.2 mg (32%) of 94: MS (ES⁺) m/z 974.49 [M+H]⁺.

(S)-tert-butyl 2-((S)-2-amino-3-methylbutanamido)propanoate (97): To a mixture of the alanine-O-tert-butyl ester hydrogen chloride salt (98) (500 mg, 2.76 mmol) in dichloromethane (5 mL) was added Fmoc-val-OSu (99) (1.09 g, 2.51 mmol). DIPEA (0.96 ml, 5.5 mmol) was added and the reaction mixture was allowed to stir at an ambient temperature for 16 h. The mixture was poured into dichloromethane (100 mL) and washed with 1N HCl (50 mL) and water (50 mL) before being dried over magnesium sulfate. The material was chromatographed on a 2 mm radial chromatotron plate eluting with 1 to 5% methanol/dichloromethane gradient and product containing fractions were combined and concentrated. The resulting residue was dissolved in dichloromethane (16 mL) and piperidine (4 mL) was added. The mixture was stirred for 10 min before being concentrated under reduced pressure. The resulting residue was chromatographed on a 2 mm plate eluting first with ammonia-saturated dichloromethane followed by 5% methanol in ammonia-saturated dichloromethane to give 494 mg (2.02 mmol, 81% for two steps) of 97: ¹H-NMR (400 MHz, CDCl₃) δ 7.78 (bs, 1H), 4.47 (m, 1H), 3.30 (d, 1H), 2.30 (m, 1H), 1.38 (d, 3H), 1.47 (s, 9H), 1.00 (d, J=7.0 Hz, 3H), 0.84 (d, J=6.9 Hz, 3H),

(S)-tert-butyl 2-((S)-2-(4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzamido)-3-methylbutanamido)propanoate (100): To a mixture of the 97 (100 mg, 0.41 mmol) and 4-maleimidobenzoic acid (101) (98 mg, 0.45 mmol) was added dichloromethane (5 mL), followed by TBTU (157 mg, 0.49 mmol) and DIPEA (212 uL, 1.23 mmol). The mixture was stirred at an ambient temperature for 16 h and then purified on a 2 mm radial chromatotron plate eluting with 50% ethyl acetate in hexanes to give 95 mg (51%) of 100: ¹H-NMR (400 MHz, CDCl₃) δ 7.85 (d, J=6.6 Hz, 2H), 7.42 (d, J=6.6 Hz, 2H), 6.81 (s, 2H), 6.38 (bs, 1H), 4.43 (m, 2H), 2.14 (sept, J=6.6 Hz, 1H), 1.41 (s, 9H), 1.31 (d, J=7.0 Hz, 3H), 0.98 (m, 6H); MS (ES⁻) m/z 441.90 [M−H]⁻.

(R)-2-((S)-2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzamido)-3-methylbutanamido)propanoic acid (53): To a mixture of 100 (47 mg, 0.11 mmol) in dichloromethane (5 mL) was added trifluoroacetic acid (5 mL) and the reaction mixture was monitored by TLC (50% ethyl acetate in hexane, after pumping down the TLC plate under high vacuum for 5 min). After 75 min, no starting material could be detected by TLC. The reaction was performed a second time using the same conditions and material from both reactions were combined and purified on a 2 mm radial chromatotron plate eluting with a gradient from 5-10% methanol in dichloromethane. The yield was 42 mg (49%) of 53: ¹H-NMR (400 MHz, CDCl₃) δ 7.92 (d, J=6.6 Hz, 2H), 7.51 (d, J=6.6 Hz, 2H), 7.0 (m, 1H), 6.89 (s, 2H), 6.70 (s, 1H), 4.60 M, 1H), 2.22 (m, 1H), 1.18 (d, J=6.6 Hz, 3H), 1.04 (m, 6H); MS (ES⁺) m/z 388.02 [M+H]⁺.

(S)-2-((S)-2-(2-iodoacetamido)-3-methylbutanamido)propanoic acid (102): To a mixture of the 97 (100 mg, 0.41 mmol) in dichloromethane was added iodoacetamide-NHS ester (103) (115 mg, 0.41 mmol) and the mixture was stirred at an ambient temperature. After 30 min, the mixture was aspirated onto a 1 mm chromototron plate and eluted with ethyl acetate in hexanes (1:1). A single band was collected and the structure was confirmed: ¹H-NMR (400 MHz, CDCl₃) δ 6.70 (d, J=7.8 Hz, 1H), 6.27 (d, J=7.0 Hz, 1H), 4.45 (m, 1H), 4.26 (dd, J=8.6, 6.3 Hz, 1H), 3.72 (quart, J=11.3 Hz, 2H), 2.13 (sept, J=6.5 Hz, 1H), 1.47 (s, 9H), 1.38 (d, J=7.1 Hz, 3H), 0.99 (m, 6H); MS (ES⁺) m/z 412.87 [M+H]⁺.

(S)-2-((S)-2-(2-iodoacetamide)-3-methylbutanamido)propanoic acid (55): See procedure for the synthesis of (R)-2-((S)-2-(4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzamido)-3-methylbutanamido)propanoic acid (53). This gave 22 mg (15% for two steps): ¹H -NMR (400 MHz, D₆-DMSO) δ 8.27 (d, J=9.4 Hz, 1H), 4.24 (m, 2H), 3.97 (bs, 2H), 3.83 (d, J=9.4 Hz, 1H), 3.71 (d, J=9.6 Hz, 1H), 2.07 (m, 1H), 1.33 (d, J=7.3 Hz, 3H), 0.93 (d, J=6.7 Hz, 3H), 0.89 (d, J=6.9 Hz, 3H); MS (ES⁻) m/z 354.84 [M−H]⁻.

PBD dimers linked through aliphatic amines (Scheme 21). PBD dimers containing aliphatic amines, such as a benzyl amine (Example 9), are synthesized with peptidic linkers, the glucuronide linker, and/or linkers dependent on mAb degradation for release (i.e., non-cleavable linkers). Drug linkers conjugated through a benzyl amine will include: (1) a cleavable peptide employing chemistry similar to Scheme 1; (2) direct attachment with a maleimidocaproyl group (a noncleavable linker) (Scheme 2); (3) a glucuronide linker, prepared as described in Scheme 6.

Generic peptide linked 2-, 3-, and 4-aniline PBD dimers (Scheme 22). PBD dimers with anilines at the 2-, 3-, and 4-positions will be conjugated to peptide-based linkers, employing the chemistry described in Scheme 1, or attached directly with maleimidocaproic acid, as exemplified in Scheme 2.

Example 14 Preparation of PDB Dimer Conjugates

Antibody-drug conjugates were prepared as previously described (see Doronina et al., Nature Biotechnology, 21, 778-784 (2003)) or as described below. Briefly, for maleimide drug-linker the mAbs (4-5 mg/mL) in PBS containing 50 mM sodium borate at pH 7.4 were reduced with tris(carboxyethyl)phosphine hydrochloride (TCEP) at 37° C. The progress of the reaction, which reduces interchain disulfides, was monitored by reaction with 5,5′-dithiobis(2-nitrobenzoic acid) and allowed to proceed until the desired level of thiols/mAb was achieved. The reduced antibody was then cooled to 0° C. and alkylated with 1.5 equivalents of maleimide drug-linker per antibody thiol. After 1 h, the reaction was quenched by the addition of 5 equivalents of N-acetyl cysteine. Quenched drug-linker was removed by gel filtration over a PD-10 column. The ADC was then sterile-filtered through a 0.22 μm syringe filter. Protein concentration was determined by spectral analysis at 280 nm and 329 nm, respectively, with correction for the contribution of drug absorbance at 280 nm. Size exclusion chromatography was used to determine the extent of antibody aggregation and RP-HPLC confirmed the absence of remaining NAC-quenched drug-linker.

For halo acetamide-based drug linkers, conjugation was performed generally as follows: To a 10 mg/mL solution of reduced and reoxidized antibody (having introduced cysteines by substitution of S239C in the heavy chains (see infra)) in 10 mM Tris (pH 7.4), 50 mM NaCl, and 2 mM DTPA was added 0.5 volumes of propylene glycol. A 10 mM solution of acetamide-based drug linker in dimethylacetamide was prepared immediately prior to conjugation. An equivalent amount of propylene glycol as added to the antibody solution was added to a 6-fold molar excess of the drug linker. The dilute drug-linker solution was added to the antibody solution and the pH was adjusted to 8.0-8.5 using 1 M Tris (pH 9). The conjugation reaction was allowed to proceed for 45 minutes at 37° C. The conjugation was verified by reducing and denaturing reversed phase PLRP-S chromatography. Excess drug linker was removed with Quadrasil MP resin (Sigma Aldrich; Product #679526) and the buffer was exchanged into 10 mM Tris (pH 7.4), 50 mM NaCl, and 5% propylene glycol using a PD-10 desalting column (GE Heathcare; Product #17-0851-01).

Engineered hIgG1 antibodies with introduced cysteines: CD70 antibodies containing a cysteine residue at position 239 of the heavy chain (h1F6d) were fully reduced by adding 10 equivalents of TCEP and 1 mM EDTA and adjusting the pH to 7.4 with 1M Tris buffer (pH 9.0). Following a 1 hour incubation at 37° C., the reaction was cooled to 22° C. and 30 equivalents of dehydroascorbic acid were added to selectively reoxidize the native disulfides, while leaving cysteine 239 in the reduced state. The pH was adjusted to 6.5 with 1M Tris buffer (pH 3.7) and the reaction was allowed to proceed for 1 hour at 22° C. The pH of the solution was then raised again to 7.4 by addition of 1 M Tris buffer (pH 9.0). 3.5 equivalents of the PBD drug linker in DMSO were placed in a suitable container for dilution with propylene glycol prior to addition to the reaction. To maintain solubility of the PBD drug linker, the antibody itself was first diluted with propylene glycol to a final concentration of 33% (e.g., if the antibody solution was in a 60 mL reaction volume, 30 mL of propylene glycol was added). This same volume of propylene glycol (30 mL in this example) was then added to the PBD drug linker as a diluent. After mixing, the solution of PBD drug linker in propylene glycol was added to the antibody solution to effect the conjugation; the final concentration of propylene glycol is 50%. The reaction was allowed to proceed for 30 minutes and then quenched by addition of 5 equivalents of N-acetyl cysteine. The ADC was then purified by ultrafiltration through a 30 kD membrane. (Note that the concentration of propylene glycol used in the reaction can be reduced for any particular PBD, as its sole purpose is to maintain solubility of the drug linker in the aqueous media.)

Example 15 Determination of In Vitro Activity of Selected Conjugates

The in vitro cytotoxic activity of the selected antibody drug conjugates was assessed using a resazurin (Sigma, St. Louis, Mo., USA) reduction assay (reference: Doronina et al., Nature Biotechnology, 2003, 21, 778-784). The antibody drug conjugates were prepared as described above in Example 13.

For the 96-hour assay, cells cultured in log-phase growth were seeded for 24 h in 96-well plates containing 150 μL RPMI 1640 supplemented with 20% FBS. Serial dilutions of ADC in cell culture media were prepared at 4× working concentration; 50 μL of each dilution was added to the 96-well plates. Following addition of ADC, the cells were incubated with test articles for 4 days at 37° C. Resazurin was then added to each well to achieve a 50 μM final concentration, and the plates were incubated for an additional 4 h at 37° C. The plates were then read for the extent of dye reduction on a Fusion HT plate reader (Packard Instruments, Meridien, Conn., USA) with excitation and emission wavelengths of 530 and 590 nm, respectively. The IC₅₀ value, determined in triplicate, is defined here as the concentration that results in a 50% reduction in cell growth relative to untreated controls.

Referring to Table 4 (infra), the in vitro cytotoxicity of ADCs having para-aniline PBD dimers using the 96 hour assay is shown. The ADCs were tested against CD70⁺ CD30⁻ cell lines and a control CD70⁻ CD30⁻ cell line. The antibodies used were a CD70 antibody, humanized 1F6 (see Published U.S. Application No. 2009-148942), a CD30 antibody, chimeric AC10 (see Published U.S. Application No. 2008-0213289) and a CD70 antibody (humanized 1F6) having introduced cysteine residues at amino acid heavy chain position 239 (according to the EU numbering system) (indicated as h1F6d). Conjugates having a maleimidyl-peptide linker (drug linker compound 38) had a lower IC₅₀ than conjugates with a maleimidyl or acetamide-based linker (compounds 40 and 41, respectively).

In vitro cytotoxic activity of ADCs bearing drug linkers derived from para-aniline PBD dimer 37:

TABLE 4 In vitro cytotoxic activity on CD70+ cell lines (ng/mL), all ADCs 2 drugs/mAb renal cell carcinoma AML CD70+/30− CD70−/30− 786-O Caki-1 769-P ACHN HEL9217 h1F6d-38 30 5 1378 h1F6-38 4 118 26 cAC10-38 1052 4005 508 h1F6-40 7113 1764 cAC10-40 2644 1264 h1F6-41 580 1243 cAC10-41 1153 1121

Referring to Table 5, the in vitro cytotoxicity of ADCs conjugate to PBD dimers on CD30⁺ cell lines using the 96 hour assay is shown. The ADCs were tested against CD30⁺CD70⁺ cell lines and a CD70⁻ CD30⁺ cell line. The antibodies used were a CD70 antibody, humanized 1F6 (see Published U.S. Application No. 2009-148942) and a CD30 antibody, chimeric AC10 (see Published U.S. Application No. 2008-0213289). Conjugates having a maleimidyl-peptide linker (drug linker compound 38) generally had a lower IC₅₀ than conjugates with a maleimidyl or acetamide-based linker (compounds 40 and 41, respectively).

TABLE 5 In vitro cytotoxic activity on CD30+ cell lines (ng/mL), all ADCs 2 drugs/mAb ALCL Hodgkin lymphoma CD70−/30+ CD70+/30+ Karpas 299 L428 L540cy L1236 Hs445 h1F6-38 1165 59 4 >10,000 5 cAC10-38 0.8 7 3 2012 0.2 h1F6-40 2195 7867 2557 cAC10-40 621 3172 134 h1F6-41 1330 3549 755 cAC10-41 340 957 13

In vitro cytotoxic activity of ADCs bearing drug linkers derived from meta-aniline PBD dimer 42:

Referring to Table 6, the in vitro cytotoxicity of ADCs containing PBD dimers on CD30⁺ cell lines using the 96 hour assay is shown. The activity was tested against CD30⁺CD70⁺ cell lines and a CD70⁻ CD30⁺ cell line. The antibodies used were a CD70 antibody, humanized 1F6 (see Published U.S. Application No. 2009-148942) and a CD70 antibody (humanized 1F6) having introduced cysteine residues at amino acid heavy chain position 239 (according to the EU numbering system) (indicated as h1F6d). Conjugates having a maleimidyl-peptide linker (drug linker compound 43) and a glucuronide linker (48) generally had a lower IC₅₀ than conjugates with a maleimidyl-based linker (compound 44).

TABLE 6 In vitro cytotoxic activity on CD70+ cell lines (ng/mL) Hodgkin renal cell carcinoma lymphoma Caki-1 786-O L428 h1F6d-43 (2 dr/mAb) 7 39 >10,000 IgG-43 (2 dr/mAb) >10,000 >10,000 h1F6-44 (3.5 dr/mAb) 1124 2142 IgG-44 (3.5 dr/mAb) 1491 1242 h1F6d-48 (2 dr/mAb) 89 4093 IgG-48 (2 dr/mAb) 2939 6376

In vitro cytotoxic activity of ADCs bearing drug linkers derived from para- and meta-aniline PBD dimers 38 and 42 (respectively):

Referring to Table 7, the in vitro cytotoxicity of ADCs containing PBD dimers on CD70⁺ cell lines using the 96 hour assay is shown. The activity was tested against CD70⁺ cell lines L428 and 786O and a CD70⁻ AML cell line. The antibodies used were a CD70 antibody, humanized 1F6 (see Published U.S. Application No. 2009-148942) and a CD70 antibody (humanized 1F6) having introduced cysteine residues at amino acid heavy chain position 239 (according to the EU numbering system) (indicated as h1F6d). Conjugates having a maleimidyl-peptide linker with a meta-aniline (drug linker compound 43) were somewhat less active than those having a maleimidyl-peptide linker with a para-aniline (drug linker compound 38). Reducing the drug loading of the meta-aniline compound to 2 per antibody reduced the activity. Conjugates with a glucuronide linker of the para-aniline compound (48) generally had a lower IC₅₀ than conjugates with a maleimidyl-based linker (compound 39). Further, an aryl maleimide of the para-aniline compound (54) has no activity on these cell lines. Further, a conjugate having a maleimidyl linker conjugated directly to compound 42 has reduced activity as compared with conjugate h1F6-43 (data not shown).

TABLE 7 In vitro cytotoxic activity on CD70+ cell lines (ng/mL) Hodgkin Renal cell lymphoma carcinina L428 786O control h1F6- 43 (4 dr/mAb) 404 11 1205 h1F6d- 43 (2 dr/mAb) Max inhib. = 40% 200  1625 h1F6d-48 (2 dr/mAb) 4093  89 1964 h1F6 54 (4 dr/mAb) No effect No effect No effect h1F6- 38 (2 dr/mAb) 230 (n = 2) 25 (n = 3)  503

In vitro cytotoxic activity of ADCs bearing drug linkers derived from aniline-linked PBD dimers

Referring to Table 8, the in vitro cytotoxicity of ADCs containing PBD dimers on CD70⁺ cell lines using the 96 hour assay is shown. The activity was tested against CD70⁺ cell lines Caki-1 and L428 and a CD70⁻ cell line. The antibody used was a CD70 antibody (humanized 1F6) having introduced cysteine residues at amino acid heavy chain position 239 (according to the EU numbering system) (indicated as h1F6d). Linkage of a PBD through an amine at the ortho position via a non-cleavable linker (compound 68) markedly reduced activity, as compared with an ADC linked via a para-aniline-linked cleavable linker (compound 54). Compounds 73 and 85, having a cleavable linker, showed comparable activity to compound 54; both of these compounds are linked via a para-aniline. Compounds with cleavable linkers requiring more stringeng cleavage, compounds 79 and 90, showed somewhat reduced activity, as compared to compound 54.

TABLE 8 In vitro cytotoxic activity on CD70+ cell lines (ng/mL) renal cell carcinoma Caki-1 786-O Control h1F6d- 68 (2 dr/mAb) 3236 3486 5501 h1F6d- 73 (2 dr/mAb) 2 7 482 h1F6d- 79 (2 dr/mAb) 24 348 5385 h1F6d- 54 (2 dr/mAb) 6 17 4665 h1F6d- 85 (2 dr/mAb) 3 5 4700 h1F6d- 90 (1.4 dr/mAb) . . . 12 47 678

In vitro cytotoxic activity of ADCs bearing drug linkers derived from aniline-linked PBD dimers

Referring to Table 9, the in vitro cytotoxicity of ADCs containing PBD dimers on CD70⁺ cell lines using the96 hour assay is shown. The activity was tested against CD70⁺ cell lines Caki-1 and L428 and two CD70⁻ leukemia cell lines. The antibodies used were a CD70 antibody, humanized 1F6 (see Published U.S. Application No. 2009-148942) and a CD70 antibody (humanized 1F6) having introduced cysteine residues at amino acid heavy chain position 239 (according to the EU numbering system) (indicated as h1F6d). Compound 56, having a cleavable linker linked to the antibody via an acetamide showed comparable activity to compound 38. A glucuronide-linked version of the meta-aniline linked PBD dimer, compound 48, demonstrated little activity in this assay. Compound 58, having five methylene groups in the PBD bridge, demonstrated comparable activity to compound 38, having three methylene groups in the PBD bridge.

TABLE 9 In vitro cytotoxic activity on CD70+ cell lines (ng/mL) Renal Cell Leukemia Caki-1 (CD70 786-O (CD70 CD70⁻ CD70⁻ ADCs #135,000) #190,000) Line 1 Line 2 h1F6d-56 3 6 1672 Max Inh = (1.8 dr/Ab) 50% h1F6d-48 Max Inh = Max Inh = No Effect No Effect (0.6 dr/Ab) 45% 35% h1F6d-58   0.5 2 1750 4847 (1.9 dr/Ab) h1F6d-38 5 15 2082 7188 (2 dr/Ab) (3-5, n = 4) (5-30, n = 4)

Example 16 Determination of In Vivo Cytotoxicity of Selected Conjugates

All studies were conducted in concordance with the Animal Care and Use Committee in a facility fully accredited by the Association for Assessment and Accreditation of Laboratory Animal Care. In vivo tolerability was first assessed to ensure that the conjugates were tolerated at clinically relevant doses. BALB/c mice were treated with escalating doses of ADC formulated in PBS with 0.01% Tween 20. Mice were monitored for weight loss following drug treatment; those that experienced 20% weight loss or other signs of morbidity were euthanized. The antibodies used were a CD70 antibody, humanized 1F6 (see Published U.S. Application No. 2009-148942) and a CD30 antibody, chimeric AC10 (see Published U.S. Application No. 2008-0213289),

Referring to FIG. 1, the results of a weight loss study are shown using cAC10-val-ala-SG3132(2) (cAC10-compound 38). A single dose of the conjugate administered at 5 mg administered either IP or IV resulted in little weight loss. A higher dose of the conjugate (15 mg/kg) caused weight loss in the mice.

Referring to FIG. 2, the results of a weight loss study are shown using h1F6-val-ala-SG3132(2) (h1F6-compound 38). A single dose of the conjugate administered at 5 mg administered IP resulted in some weight loss. A higher dose of the conjugate (10 mg/kg) caused significant weight loss in the mice.

Treatment studies were conducted in two CD70⁺ renal cell carcinoma xenograft models. Tumor (786-O and Caki-1) fragments were implanted into the right flank of Nude mice. Mice were randomized to study groups (n=5) on day eight (786-O) or nine (Caki-1) with each group averaging around 100 mm³. The ADC or controls were dosed ip according to a q4dx4 schedule. Tumor volume as a function of time was determined using the formula (L×W²)/2. Animals were euthanized when tumor volumes reached 1000 mm³. Mice showing durable regressions were terminated around day 100 post implant.

Referring to FIG. 3, the results of a treatment study using an h1F6-val-ala-SG3132(2) (h1F6-compound 38) conjugate are shown. A control conjugate, cAC10-val-ala-SG3132(2) (cAC10-compound 38), was also used. Mice administered doses of the h1F6 conjugate at 0.1 mg/kg exhibited some tumor reduction, while higher doses at 0.3 mg/kg and 1 mg/kg appeared to exhibit complete tumor reduction. The control conjugate (non-binding) was less active the h1F6 conjugates.

Referring to FIG. 4, the results of a treatment study using an h1F6-mc-val-ala-SG3132(2) (h1F6-compound 38) conjugate are shown. A control conjugate, cAC10-mc-val-ala-SG3132(2) (cAC10-compound 38), was also used. Mice administered doses of the h1F6 conjugate at 1 mg/kg appeared to exhibit complete tumor reduction. Mice administered lower doses at 0.3 mg/kg and 0.1 mg/kg exhibited lesser tumor reduction, respectively. The control conjugate (non-binding) was less active the h1F6 conjugate administered at a similar dose, although it exhibited more activity than the h1F6 conjugate administered at lower doses. The h1F6 conjugate was also more active than an h1F6-vc-MMAE conjugate (Published U.S. Application No. 2009-0148942) administered at higher doses.

Referring to FIG. 5, the results of a treatment study using a two loaded antibody h1F6d-linked to compound 38 (h1F6d-38) compared to a two-loaded non-binding control, H00d conjugated to the same compound (h00d-38). The model was a Caki subcutaneous model in Nude mice. Doses were 0.1, 0.3 and 1 mg/kg q7dX2. The highest two doses of the h1F6 conjugate demonstrated complete regressions as 1 mg/kg and substantial tumor delay at 0.3 mg/kg. The non-binding control demonstrated tumor delay at the 1 mg/kg dose.

Referring to FIG. 6, the results of a treatment study using a two loaded antibody h1F6d-linked to compound 38 (h1F6d-38) compared to a two-loaded non-binding control, H00d conjugated to the same compound (h00d-38). The model was a 786-O subcutaneous model in Nude mice. Doses were 0.1, 0.3 and 1 mg/kg q7dX2. All three doses or the h1F6 conjugate demonstrated complete regressions or tumor delay, while the non-binding control demonstated tumor delay. 

1. A conjugate having formula I: L-(LU-D)_(p)   (I) or a pharmaceutically acceptable salt thereof; wherein L is a Ligand unit selected from the group consisting of an antibody, an antigen-binding fragment of an antibody and a Fc fusion protein, LU is a Linker unit of formula Ia: -A¹-L¹-,   (1a) wherein: L¹ is an amino acid sequence comprising a dipeptide of formula —NH—X₁-X₂—CO—, wherein —NH— is the amino group of X₁, and CO is the carbonyl group of X₂, and wherein the peptide is cleavable by the action of an enzyme to release fee drug, wherein the enzyme is a cathepsin; A¹ is a Stretcher Unit, wherein A¹ comprises the functionality —CO— connected directly to the amino terminus of X₁ thereby to form an amide link with —X₁— and wherein A₁ is further comprised of the structure:

wherein the wavy line indicates the point of attachment to the Ligand unit wherein S is a sulfur atom derived from the Ligand Unit, and the asterisk indicates the bond to the remaining portion of A¹: p is 1 to 20; and D is a Drug unit wherein the Drug unit is a PBD dimer having the following formula II:

wherein: R² is of formula III:

wherein A is a C₅₋₇ aryl group, X is connected to the Linker unit and is selected from the group consisting of —O—, —S—, —C(O)O—, —C(O)—, —NH(C═O)—, and —N(R^(N))—, wherein R^(N) is selected from the group consisting of H, C₁₋₄ alkyl and (C₂H₄O)_(m)CH₃, where m is 1 to 3, and either: (i) Q¹ is a single bond, and Q² is selected from the group consisting of a single bond and —Z—(CH₂)_(n)—, wherein Z is selected from the group consisting of a single bond, O, S and NH and n is from 1 to 3, or (ii) Q¹ is —CH═CH— and Q² is a single bond; R¹² is a C₅₋₁₀ aryl group optionally substituted by one or more substituents selected from the group consisting of halo, nitro, cyano, C₁₋₇ alkoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are independently selected from the group consisting of H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo; R⁷ is selected from the group consisting of H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo; wherein R and R′ are independently selected from the group consisting of optionally substituted C₁₋₁₂ alkyl, C₃₋₂₀ heterocyclyl, and C₅₋₂₀ aryl groups; either: (a) R¹⁰ is H, and R¹¹ is OH, OR^(A), wherein R^(A) is C₁₋₄ alkyl, or (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, or (c) R¹⁰ is H and R¹¹ is SO_(z)M, wherein z is 2; R″ is a C₃₋₁₂ alkylene group optionally interrupted by one or more heteroatoms selected from the group consisting of O, S, and NH, or by an aromatic ring; Y and Y′ are selected from the group consisting of O, S, and NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively, and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, and each M is a monovalent pharmaceutically acceptable cation or both M groups together are a divalent pharmaceutically acceptable cation; wherein C₃₋₂₀ heterocyclyl is a monovalent moiety obtained by removing a hydrogen atom of a heterocyclic compound which has 3 to 20 ring atoms, of which 1 to 10 are heteroatoms selected from the group consisting of N, O and S; and wherein C₃₋₇ heterocyclyl is a monovalent moiety obtained by removing a hydrogen atom of a heterocyclic compound which has 3 to 7 ring atoms, of which 1 to 4 are heteroatoms selected from the group consisting of N, O and S.
 2. The conjugate according to claim 1 wherein the dipeptide of formula —NH—X₁-X₂—CO—, is selected from the group consisting of -Phe-Lys-,-Val-Ala-, -Val-Lys-, -Ala-Lys-, -Val-Cit-,-Phe-Cit-, -Leu-Cit-, -Ile-Cit-, -Phe-Arg-, and -Trp-Cit-, wherein Cit is citrulline.
 3. The conjugate according to claim 1 wherein A¹ is selected from the group consisting of:

wherein the asterisk indicates the point of attachment to the amino group of X₁, the wavy line indicates the point of attachment to the Ligand unit, n is 0 or 1, and m is 0 to 30; and

wherein the asterisk indicates the point of attachment to the amino group of X₁, the wavy line indicates the point of attachment to the Ligand unit, n is 0 or 1, and m is 0 to
 30. 4. The conjugate according to claim 2, wherein R⁷ is selected from the group consisting of H, OH and OR.
 5. The conjugate according to claim 2, wherein R⁷ is a C₁₋₄ alkyloxy group.
 6. The conjugate according to claim 4, wherein Y and Y′ are O.
 7. The conjugate according to claim 6, wherein R″ is C₃₋₇ alkylene.
 8. The conjugate according to claim 7, wherein R⁹ is H.
 9. The conjugate according to claim 8, wherein R⁶ is selected from the group consisting of H and halo.
 10. The conjugate according to claim 1, wherein A is phenyl, X is selected from the group consisting of —O—, —S—, and —NH—, and Q¹ is a single bond.
 11. The conjugate according to claim 10, wherein X is NH.
 12. The conjugate according to claim 11, wherein Q¹ is a single bond and Q² is a single bond.
 13. The conjugate according to claim 1, wherein R¹² is a C₅₋₇ aryl group optionally substituted by one or more substituents selected from the group consisting of halo, nitro, cyano, C₁₋₇ alkoxy, C₅₋₂₀ aryloxy, C₃₋₂₀ heterocyclyoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene wherein the C₁₋₇ alkoxy group is optionally substituted by an amino group, and if the C₃₋₇ heterocyclyl group is a C₆ nitrogen containing heterocyclyl group, it is optionally substituted by a C₁₋₄ alkyl group.
 14. The conjugate according to claim 13, wherein the C₆₋₇ aryl group is an optionally substituted phenyl group.
 15. The conjugate according to claim 14, wherein R¹² bears one to three substituent groups.
 16. The conjugate according to claim 1, wherein R¹⁰ and R¹¹ form a nitrogen-carbon double bond.
 17. The conjugate according to claim 1, wherein R^(6′), R^(7′), R^(9′), and Y′ are the same as R⁶, R⁷, R⁹, and Y respectively.
 18. The conjugate according to claim 1 wherein D has the formula:

wherein the wavy line of D indicates covalent attachment to LU and A¹ is selected from the group consisting of:

wherein the asterisk indicates the point of attachment to the amino group of X₁, the wavy line to A¹ indicates the point of attachment to the Ligand unit, n is 0 or 1, and m is 0 to 30; and

wherein the asterisk indicates the point of attachment to the amino group of X₁, the wavy line indicates the point of attachment to the Ligand unit, n is 0 or 1, and m is 0 to
 30. 19. The conjugate according to claim 18 wherein D has the formula:


20. The conjugate according to claim 18 wherein D has the formula:


21. The conjugate according to claim 19 wherein the Ligand unit is an antibody and wherein the sulfur atom bonding the antibody Ligand Unit to A¹ of the Linker unit is from a thiol group of a cysteine residue of the antibody.
 22. The conjugate according to claim 21 wherein the cysteine residue is an introduced cysteine residue in the heavy chain or light chain of the antibody or antigen binding fragment thereof.
 23. The conjugate according to claim 22 wherein the introduced cysteine is at amino acid heavy chain position 239, according to the EU numbering system.
 24. The conjugate according to claim 21 wherein the antibody is a humanized 1F6 antibody
 25. The conjugate according to claim 23 wherein the antibody is a humanized 1F6 antibody.
 26. A Drug Linker having the formula: G¹-L¹-D or a salt thereof; wherein L¹ is an amino acid sequence comprising a dipeptide of formula —NH—X₁-X₂—CO—, wherein —NH— is the amino group of X₁, and CO is the carbonyl group of X₂, and wherein the peptide is cleavable by the action of an enzyme to release fee drug, wherein the enzyme is a cathepsin; G¹ is a Stretcher Unit to form a connection to a Ligand unit, wherein G¹ is comprised of a maleimide group for reaction with a thiol group on the Ligand unit for said connection, and wherein G¹ further comprises the functionality —CO— connected directly to the amino terminus of X₁ thereby to form an amide link with —X₁— and D is a Drug unit wherein the Drug unit is a PBD dimer having the following formula II:

wherein: R² is of formula III:

wherein A is a C₅₋₇ aryl group, X is connected to the Linker unit and is selected from the group consisting of —O—, —S—, —C(O)O—, —C(O)—, —NH(C═O)—, and —N(R^(N))—, wherein R^(N) is selected from the group consisting of H, C₁₋₄ alkyl and (C₂H₄O)_(m)CH₃, where m is 1 to 3, and either: (i) Q¹ is a single bond, and Q² is selected from the group consisting of a single bond and —Z—(CH₂)_(n)—, wherein Z is selected from the group consisting of a single bond, O, S and NH and n is from 1 to 3, or (ii) Q¹ is —CH═CH— and Q² is a single bond; R¹² is a C₅₋₁₀ aryl group, optionally substituted by one or more substituents selected from the group consisting of halo, nitro, cyano, C₁₋₇ alkoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are independently selected from the group consisting of H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo; R⁷ is selected from the group consisting of H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo; wherein R and R′ are independently selected from the group consisting of optionally substituted C₁₋₁₂ alkyl, C₃₋₂₀ heterocyclyl, and C₅₋₂₀ aryl groups; either; (a) R¹⁰ is H, and R¹¹ is OH, OR^(A), wherein R^(A) is C₁₋₄ alkyl, or (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, or (c) R¹⁰ is H and R¹¹ is SO_(z)M, wherein z is 2; R″ is a C₃₋₁₂ alkylene group, which chain is optionally interrupted by one or more heteroatoms, selected from the group consisting of O, S, and NH, or by an aromatic ring; Y and Y′ are selected from the group consisting of O, S, and NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively, and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹ and each M is a monovalent pharmaceutically acceptable cation or both M groups together are a divalent pharmaceutically acceptable cation; wherein C₃₋₂₀ heterocyclyl is a monovalent moiety obtained by removing a hydrogen atom of a heterocyclic compound which has 3 to 20 ring atoms, of which 1 to 10 are heteroatoms selected from the group consisting of N, O and S; and wherein C₃₋₇ heterocyclyl is a monovalent moiety obtained by removing a hydrogen atom of a heterocyclic compound which has 3 to 7 ring atoms, of which 1 to 4 are heteroatoms selected from the group consisting of N, O and S.
 27. The Drug Linker according to claim 26 wherein the dipeptide of formula —NH—X₁-X₂—CO—, is selected from the group consisting of -Phe-Lys-,-Val-Ala-, -Val-Lys-, -Ala-Lys-, -Val-Cit-,-Phe-Cit-, -Leu-Cit-, -Ile-Cit-, -Phe-Arg-, and -Trp-Cit-, wherein Cit is citrulline.
 28. The Drug Linker according to claim 26, wherein G¹ is selected from the group consisting of:

wherein the asterisk indicates the point of attachment to the a group of X₁, n is 0 or 1, and m is 0 to 30; and

wherein the asterisk indicates the point of attachment to the amino group of n is 0 or 1, and m is 0 to
 30. 29. The Drug linker according to claim 27, wherein R⁷ is selected from the group consisting of H, OH and OR.
 30. The Drug linker according to claim 27, wherein R⁷ is a C₁₋₄ alkyloxy group.
 31. The Drug linker according to claim 30, wherein Y and Y′ are O.
 32. The Drug linker according to claim 31, wherein R″ is C₃₋₇ alkylene.
 33. The Drug linker according to claim 32, wherein R⁹ is H.
 34. The Drug linker according to claim 33, wherein R⁶ is selected from the group consisting of H and halo.
 35. The Drug linker according to claim 26, wherein A is phenyl, X is selected from the group consisting of —O—, —S—, and —NH—, and Q¹ is a single bond.
 36. The Drug linker according to claim 35, wherein X is NH.
 37. The Drug linker according to claim 36, wherein Q¹ is a single bond and Q² is a single bond.
 38. The Drug linker according to claim 26, wherein R¹² is a C₅₋₇ aryl group optionally substituted by one or more substituents selected from the group consisting of halo, nitro, cyano, C₁₋₇ alkoxy, C₅₋₂₀ aryloxy, C₃₋₂₀ heterocyclyoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene wherein the C₁₋₇ alkoxy group is optionally substituted by an amino group, and if the C₃₋₇ heterocyclyl group is a C₆ nitrogen containing heterocyclyl group, it is optionally substituted by a C₁₋₄ alkyl group.
 39. The Drug linker according to claim 38, wherein the C₅₋₇ aryl group is an optionally substituted phenyl group.
 40. The Drug linker according to claim 39, wherein R¹² bears one to three substituent groups.
 41. The Drug linker according to claim 26, wherein R¹⁰ and R¹¹ form a nitrogen-carbon double bond.
 42. The Drug linker according to claim 26, wherein R^(6′), R^(7′), R^(9′), and Y′ are the same as R⁶, R⁷, R⁹, and Y respectively.
 43. The Drug linker according to claim 26 wherein D has the formula:

wherein the wavy line of D indicates covalent attachment to LU.
 44. The Drug linker according to claim 43 wherein D has the formula:

wherein the wavy line of D indicates covalent attachment to LU.
 45. The Drug linker according to claim 43 wherein D has the formula:

wherein the wavy line of D indicates covalent attachment to LU.
 46. The Drug linker according to claim 26, wherein the Drug linker has the formula of:


47. A method of treating a mammal having a proliferative disease wherein the cell surface antigen bound by the Ligand unit is expressed by proliferative cells of the proliferative disease comprising administering an effective amount of the conjugate of claim 1, wherein the proliferative disease treated is selected from the group consisting of renal cell carcinoma, Hodgkin Lymphoma, anaplastic large cell lymphoma and leukemia. 